kcp: update config parser to load value of KCP

this was missed in 37a714e7 where the value of kcp
was written to the config file but during  parsing
the value was not added to the local struct

pkg/config/gui.go

@@ -80,6 +80,7 @@ func ParseConfig() *Config {
 	conf.StartVPN = !conf.file.UserStoppedVPN
 	conf.UDP = conf.file.UDP
 	conf.Snowflake = conf.file.Snowflake
+	conf.KCP = conf.file.KCP
 	return &conf
 }