Merge pull request #29768 from Mic92/networkd

networkd: also load builtin modules

nixos/modules/system/boot/networkd.nix

···
   unitFiles = map (name: {
     target = "systemd/network/${name}";
     source = "${cfg.units.${name}.unit}/${name}";
-  }) (attrNames cfg.units);
+  }) (attrNames cfg.units) ++
+  (map (entry: {
+    target = "systemd/network/${entry}";
+    source = "${config.systemd.package}/lib/systemd/network/${entry}";
+  }) (attrNames (builtins.readDir "${config.systemd.package}/lib/systemd/network")));
 in
 
 {