ip4-config: keep track of ifindex

No functional change, a cosmetic thing for now.

We want it set before any routes are added and ensure routes have a valid
ifindex before we pass it to the platform.

In a future NMRouteManager will need to look up the route for a device in
its cache thus we'll need to make sure routes passed to the it have an
appropriate ifindex set.

src/dhcp-manager/nm-dhcp-systemd.c

@@ -206,7 +206,8 @@ G_STMT_START { \
 } G_STMT_END
 
 static NMIP4Config *
-lease_to_ip4_config (sd_dhcp_lease *lease,
+lease_to_ip4_config (const char *iface,
+                     sd_dhcp_lease *lease,
                      GHashTable *options,
                      guint32 default_priority,
                      gboolean log_lease,
@@ -387,7 +388,7 @@ nm_dhcp_systemd_get_lease_ip_configs (const char *iface,
 	path = get_leasefile_path (iface, uuid, FALSE);
 	r = sd_dhcp_lease_load (&lease, path);
 	if (r == 0 && lease) {
-		ip4_config = lease_to_ip4_config (lease, NULL, default_route_metric, FALSE, NULL);
+		ip4_config = lease_to_ip4_config (iface, lease, NULL, default_route_metric, FALSE, NULL);
 		if (ip4_config)
 			leases = g_slist_append (leases, ip4_config);
 	}
@@ -440,7 +441,8 @@ bound4_handle (NMDhcpSystemd *self)
 	}
 
 	options = g_hash_table_new_full (g_str_hash, g_str_equal, NULL, g_free);
-	ip4_config = lease_to_ip4_config (lease,
+	ip4_config = lease_to_ip4_config (iface,
+	                                  lease,
 	                                  options,
 	                                  nm_dhcp_client_get_priority (NM_DHCP_CLIENT (self)),
 	                                  TRUE,