fix: Update DNS behavior for NetworkManager interfaces

If DNS information is added to a NetworkManager managed interface where
the given protocol family is disabled, NetworkManager will be unable to
activate the interface. This seems like a potential bug in NetworkManager
but this fix should work around this condition which can arise in the case
of bonded interfaces where the bond members have no IP information.

cloudinit/net/network_manager.py

@@ -239,7 +239,8 @@ def _add_nameserver(self, dns: str) -> None:
         Extends the ipv[46].dns property with a name server.
         """
         family = "ipv6" if is_ipv6_address(dns) else "ipv4"
-        if self.config.has_section(family):
+        if self.config.has_section(family) \
+            and self._get_config_option(family, "method") != "disabled":
             self._set_default(family, "dns", "")
             self.config[family]["dns"] = self.config[family]["dns"] + dns + ";"
 
@@ -248,7 +249,8 @@ def _add_dns_search(self, dns_search: List[str]) -> None:
         Extends the ipv[46].dns-search property with a name server.
         """
         for family in ["ipv4", "ipv6"]:
-            if self.config.has_section(family):
+            if self.config.has_section(family) \
+                and self._get_config_option(family, "method") != "disabled":
                 self._set_default(family, "dns-search", "")
                 self.config[family]["dns-search"] = (
                     self.config[family]["dns-search"]