platform: fix returning error from nm_platform_ip_address_sync()

None of the callers really handle the return value of nm_platform_ip_address_sync()
or whether the function encountered problems. What would they anyway do
about that?

For IPv4 we were already ignoring errors to add addresses, but for IPv6 we
aborted. That seems wrong. As the caller does not really handle errors,
I think we should follow through and add all addresses in case of error.

Still, also collect a overall "success" of the function and return it.

src/libnm-platform/nm-platform.c

@@ -3941,14 +3941,9 @@ ip6_address_scope_cmp(gconstpointer p_a, gconstpointer p_b, gpointer increasing)
  * @self: platform instance
  * @addr_family: the address family AF_INET or AF_INET6.
  * @ifindex: Interface index
- * @known_addresses: List of addresses. The list will be modified and only
+ * @known_addresses: List of addresses. The list will be modified and
- *   addresses that were successfully added will be kept in the list.
+ *   expired addresses will be cleared (by calling nmp_object_unref()
- *   That means, expired addresses and addresses that could not be added
+ *   on the array element).
- *   will be dropped.
- *   Hence, the input argument @known_addresses is also an output argument
- *   telling which addresses were successfully added.
- *   Addresses are removed by unrefing the instance via nmp_object_unref()
- *   and leaving a NULL tombstone.
  * @addresses_prune: (allow-none): the list of addresses to delete.
  *   If platform has such an address configured, it will be deleted
  *   at the beginning of the sync. Note that the array will be modified
@@ -3975,6 +3970,7 @@ nm_platform_ip_address_sync(NMPlatform *self,
     gs_unref_hashtable GHashTable *known_addresses_idx = NULL;
     gs_unref_ptrarray GPtrArray   *plat_addresses      = NULL;
     GHashTable                    *known_subnets       = NULL;
+    gboolean                       success;
     guint                          i_plat;
     guint                          i_know;
     guint                          i;
@@ -4145,7 +4141,7 @@ nm_platform_ip_address_sync(NMPlatform *self,
                                        ip6_address_scope_cmp,
                                        GINT_TO_POINTER(FALSE));
 
-            known_addresses_len = known_addresses ? known_addresses->len : 0;
+            known_addresses_len = nm_g_ptr_array_len(known_addresses);
 
             /* First, check that existing addresses have a matching plen as the ones
              * we are about to configure (@known_addresses). If not, delete them. */
@@ -4246,6 +4242,8 @@ next_plat:;
     if (IS_IPv4)
         ip4_addr_subnets_destroy_index(known_subnets, known_addresses);
 
+    success = TRUE;
+
     /* Add missing addresses. New addresses are added by kernel with top
      * priority.
      */
@@ -4281,9 +4279,8 @@ next_plat:;
                     lifetime,
                     preferred,
                     IFA_F_NOPREFIXROUTE,
-                    known_address->a4.label)) {
+                    known_address->a4.label))
-                /* ignore error, for unclear reasons. */
+                success = FALSE;
-            }
         } else {
             if (!nm_platform_ip6_address_add(self,
                                              ifindex,
@@ -4293,11 +4290,11 @@ next_plat:;
                                              lifetime,
                                              preferred,
                                              IFA_F_NOPREFIXROUTE | known_address->a6.n_ifa_flags))
-                return FALSE;
+                success = FALSE;
         }
     }
 
-    return TRUE;
+    return success;
 }
 
 gboolean