change output references from attrset to lambda

this is so that we can distinguish a ref from a literal parameter that
might be a attrset

modules/hostapd/service.nix

@@ -30,7 +30,7 @@ let
   literal_or_output = o: ({
     string = builtins.toJSON;
     int = builtins.toJSON;
-    set = (o: "output(${builtins.toJSON o.service}, ${builtins.toJSON o.path})");
+    lambda = (o: "output(${builtins.toJSON (o "service")}, ${builtins.toJSON (o "path")})");
   }.${builtins.typeOf o}) o;
 
   conf =