lib/modules.nix: Optimize optionSet legacy compat code

It's still in the hot path.

lib/modules.nix

@@ -761,13 +761,13 @@ rec {
       options = opt.options or
         (throw "Option `${showOption loc}' has type optionSet but has no option attribute, in ${showFiles opt.declarations}.");
       f = tp:
-        let optionSetIn = type: (tp.name == type) && (tp.functor.wrapped.name == "optionSet");
-        in
         if tp.name == "option set" || tp.name == "submodule" then
           throw "The option ${showOption loc} uses submodules without a wrapping type, in ${showFiles opt.declarations}."
-        else if optionSetIn "attrsOf" then types.attrsOf (types.submodule options)
-        else if optionSetIn "listOf"  then types.listOf  (types.submodule options)
-        else if optionSetIn "nullOr"  then types.nullOr  (types.submodule options)
+        else if (tp.functor.wrapped.name or null) == "optionSet" then
+          if tp.name == "attrsOf" then types.attrsOf (types.submodule options)
+          else if tp.name == "listOf" then types.listOf  (types.submodule options)
+          else if tp.name == "nullOr" then types.nullOr  (types.submodule options)
+          else tp
         else tp;
     in
       if opt.type.getSubModules or null == null