message: remove unnecessary yield in TCP manager's poll task
  Tokio will handle dead loop properly.
diff: @@ -223,8 +223,6 @@ impl TcpTun {
  next_duration
  };
  - tokio::task::yield_now().await;
  -
  tokio::select! {
  _ = time::sleep(StdDuration::from(next_duration)) => {}
  _ = manager_notify.notified() => {}
  