networkd: merge DNS and NTP entries when exporting

In the state files, do not distinguish where the various entries came from
(static or DHCP), but include them all in the same list.

src/network/networkd-network.c

@@ -169,15 +169,8 @@ void network_free(Network *network) {
         free(network->description);
         free(network->dhcp_vendor_class_identifier);
 
-        while ((address = network->ntp)) {
-                LIST_REMOVE(addresses, network->ntp, address);
-                address_free(address);
-        }
-
-        while ((address = network->dns)) {
-                LIST_REMOVE(addresses, network->dns, address);
-                address_free(address);
-        }
+        strv_free(network->ntp);
+        strv_free(network->dns);
 
         netdev_unref(network->bridge);