chore: no longer used net.DefaultResolver when dns section is disabled, now is equally only "system://"

dns/patch_android.go

@@ -12,6 +12,12 @@ func FlushCacheWithDefaultResolver() {
 	if r := resolver.DefaultResolver; r != nil {
 		r.ClearCache()
 	}
+	if r := resolver.ProxyServerHostResolver; r != nil {
+		r.ClearCache()
+	}
+	if r := resolver.SystemResolver; r != nil {
+		r.ClearCache()
+	}
 	resolver.ResetConnection()
 }