message: fix Socket::cancel bug
diff: @@ -1636,7 +1636,7 @@ bool Socket::cancel(const enum swEvent_type event)
  read_co->resume();
  return true;
  }
  - else if (event == SW_EVENT_READ)
  + else if (event == SW_EVENT_WRITE)
  {
  set_err(ECANCELED);
  write_co->resume();
  