message: Remove cross-coroutine closure feature
diff: @@ -937,6 +937,10 @@ Socket* Socket::accept()
  bool Socket::shutdown(int __how)
  {
  + if (unlikely(!is_available()))
  + {
  + return false;
  + }
  if (__how == SHUT_RD && !shutdown_read)
  {
  if (::shutdown(socket->fd, SHUT_RD) == 0)
  @@ -967,7 +971,10 @@ bool Socket::shutdown(int __how)
  bool Socket::close()
  {
  - // TODO: waiting on review
  + if (unlikely(!is_available()))
  + {
  + return false;
  + }
  if (!socket->closed)
  {
  socket->closed = 1;
  