implement ifwait trigger service and use in bridge

should we convert all ifwait uses to this trigger too? seems
reasonable

modules/ifwait/ifwait.nix

@@ -0,0 +1,15 @@
+{ ifwait, liminix } :
+{
+  state
+, interface
+, service
+}:
+let
+  inherit (liminix.services) longrun;
+in longrun {
+  name = "ifwait.${interface.name}";
+  buildInputs = [ service ];
+  run = ''
+    ${ifwait}/bin/ifwait -s ${service.name}  $(output ${interface} ifname) ${state}
+  '';
+}