Update async

Netch/Controllers/NFController.cs

@@ -76,9 +76,9 @@ public class NFController : IModeController
             throw new MessageException("Redirector start failed.");
     }
 
-    public async Task StopAsync()
+    public Task StopAsync()
     {
-        await FreeAsync();
+        return FreeAsync();
     }
 
     #region CheckRule