1d61efb7f1 accidentially changed the
restartTriggers of systemd-networkd.service` to point to the attribute
name (in this case, a location relative to `/etc`), instead of the
location of the network-related unit files in the nix store.
This caused systemd-networkd to not get restarted on activation of new
networking config, if the file name hasn't changed.
Fix this, by pointing this back to the location in the nix store.
14395cc687