network/link: update state file when master ifindex is changed

If master ifindex is non-zero, then the carrier state and operational
state of the interface may be the enslaved state.
As the operational state is saved in link state file, and read by
wait-online, we need to update the state file when the master ifindex is
changed.

src/network/networkd-link.c

@@ -2223,6 +2223,9 @@ static int link_update_master(Link *link, sd_netlink_message *message) {
 
                 link_drop_from_master(link);
                 link->master_ifindex = master_ifindex;
+
+                /* Updating master ifindex may cause operational state change, e.g. carrier <-> enslaved */
+                link_dirty(link);
         }
 
         r = link_append_to_master(link);