Fix ipv6 error

(cherry picked from commit 86572cc960)

lib/fragments/config.dart

@@ -82,9 +82,7 @@ class _ConfigFragmentState extends State<ConfigFragment> {
               onChanged: (bool value) async {
                 final appController = globalState.appController;
                 appController.clashConfig.ipv6 = value;
-                await appController.updateClashConfig(
-                  isPatch: false,
-                );
+                appController.updateClashConfigDebounce();
               },
             ),
           );

lib/models/clash_config.dart

@@ -190,7 +190,7 @@ class ClashConfig extends ChangeNotifier {
 
   set ipv6(bool value) {
     if (_ipv6 != value) {
-      ipv6 = value;
+      _ipv6 = value;
       notifyListeners();
     }
   }