device: get_connection_parent() accept incomplete connections

All of these are wrong asserting that a connection has a particular
setting. On AddAndActivate, the connection can be pretty much empty:

  impl_manager_add_and_activate_connection ()
    validate_activation_request ()
      nm_manager_get_best_device_for_connection ()
      iface = nm_manager_get_connection_iface ()
        find_parent_device_for_connection ()
          nm_device_factory_get_connection_parent () <====== *shriek*
        nm_device_factory_get_connection_iface ()
      find_device_by_iface (iface)
    nm_device_complete_connection ()

Remove those assertions.

src/core/devices/nm-device-6lowpan.c

@@ -276,9 +276,10 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_6LOWPAN_SETTING_NAME), NULL);
 
     s_6lowpan = NM_SETTING_6LOWPAN(nm_connection_get_setting(connection, NM_TYPE_SETTING_6LOWPAN));
-    g_assert(s_6lowpan);
+    if (s_6lowpan)
-
+        return nm_setting_6lowpan_get_parent(s_6lowpan);
-    return nm_setting_6lowpan_get_parent(s_6lowpan);
+    else
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-infiniband.c

@@ -464,9 +464,10 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
                          NULL);
 
     s_infiniband = nm_connection_get_setting_infiniband(connection);
-    g_assert(s_infiniband);
+    if (s_infiniband)
-
+        return nm_setting_infiniband_get_parent(s_infiniband);
-    return nm_setting_infiniband_get_parent(s_infiniband);
+    else
+        return NULL;
 }
 
 static char *

src/core/devices/nm-device-ip-tunnel.c

@@ -1369,9 +1369,10 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
                          NULL);
 
     s_ip_tunnel = nm_connection_get_setting_ip_tunnel(connection);
-    g_assert(s_ip_tunnel);
+    if (s_ip_tunnel)
-
+        return nm_setting_ip_tunnel_get_parent(s_ip_tunnel);
-    return nm_setting_ip_tunnel_get_parent(s_ip_tunnel);
+    else
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-ipvlan.c

@@ -444,18 +444,18 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_IPVLAN_SETTING_NAME), NULL);
 
     s_ipvlan = _nm_connection_get_setting(connection, NM_TYPE_SETTING_IPVLAN);
-    nm_assert(s_ipvlan);
+    if (s_ipvlan) {
-
+        parent = nm_setting_ipvlan_get_parent(s_ipvlan);
-    parent = nm_setting_ipvlan_get_parent(s_ipvlan);
+        if (parent)
-    if (parent)
+            return parent;
-        return parent;
+    }
 
     /* Try the hardware address from the IPVLAN connection's hardware setting */
     s_wired = nm_connection_get_setting_wired(connection);
     if (s_wired)
         return nm_setting_wired_get_mac_address(s_wired);
-
+    else
-    return NULL;
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-macsec.c

@@ -1022,18 +1022,18 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_MACSEC_SETTING_NAME), NULL);
 
     s_macsec = nm_connection_get_setting_macsec(connection);
-    g_assert(s_macsec);
+    if (s_macsec) {
-
+        parent = nm_setting_macsec_get_parent(s_macsec);
-    parent = nm_setting_macsec_get_parent(s_macsec);
+        if (parent)
-    if (parent)
+            return parent;
-        return parent;
+    }
 
     /* Try the hardware address from the MACsec connection's hardware setting */
     s_wired = nm_connection_get_setting_wired(connection);
     if (s_wired)
         return nm_setting_wired_get_mac_address(s_wired);
-
+    else
-    return NULL;
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-macvlan.c

@@ -590,18 +590,18 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_MACVLAN_SETTING_NAME), NULL);
 
     s_macvlan = nm_connection_get_setting_macvlan(connection);
-    g_assert(s_macvlan);
+    if (s_macvlan) {
-
+        parent = nm_setting_macvlan_get_parent(s_macvlan);
-    parent = nm_setting_macvlan_get_parent(s_macvlan);
+        if (parent)
-    if (parent)
+            return parent;
-        return parent;
+    }
 
     /* Try the hardware address from the MACVLAN connection's hardware setting */
     s_wired = nm_connection_get_setting_wired(connection);
     if (s_wired)
         return nm_setting_wired_get_mac_address(s_wired);
-
+    else
-    return NULL;
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-ppp.c

@@ -380,9 +380,10 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     nm_assert(nm_connection_is_type(connection, NM_SETTING_PPPOE_SETTING_NAME));
 
     s_pppoe = nm_connection_get_setting_pppoe(connection);
-    nm_assert(s_pppoe);
+    if (s_pppoe)
-
+        return nm_setting_pppoe_get_parent(s_pppoe);
-    return nm_setting_pppoe_get_parent(s_pppoe);
+    else
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(

src/core/devices/nm-device-vlan.c

@@ -618,18 +618,18 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_VLAN_SETTING_NAME), NULL);
 
     s_vlan = nm_connection_get_setting_vlan(connection);
-    g_assert(s_vlan);
+    if (s_vlan) {
-
+        parent = nm_setting_vlan_get_parent(s_vlan);
-    parent = nm_setting_vlan_get_parent(s_vlan);
+        if (parent)
-    if (parent)
+            return parent;
-        return parent;
+    }
 
     /* Try the hardware address from the VLAN connection's hardware setting */
     s_wired = nm_connection_get_setting_wired(connection);
     if (s_wired)
         return nm_setting_wired_get_mac_address(s_wired);
-
+    else
-    return NULL;
+        return NULL;
 }
 
 static char *

src/core/devices/nm-device-vxlan.c

@@ -777,9 +777,10 @@ get_connection_parent(NMDeviceFactory *factory, NMConnection *connection)
     g_return_val_if_fail(nm_connection_is_type(connection, NM_SETTING_VXLAN_SETTING_NAME), NULL);
 
     s_vxlan = nm_connection_get_setting_vxlan(connection);
-    g_assert(s_vxlan);
+    if (s_vxlan)
-
+        return nm_setting_vxlan_get_parent(s_vxlan);
-    return nm_setting_vxlan_get_parent(s_vxlan);
+    else
+        return NULL;
 }
 
 NM_DEVICE_FACTORY_DEFINE_INTERNAL(