code: func (l *tcpListener) Close() error {
  	m := channelForwardMsg{
  		l.laddr.IP.String(),
  		uint32(l.laddr.Port),
  	}
  
  	// this also closes the listener.
  	l.conn.forwards.remove(*l.laddr)
  	ok, _, err := l.conn.SendRequest("cancel-tcpip-forward", true, Marshal(&m))
  	if err == nil && !ok {
  		err = errors.New("ssh: cancel-tcpip-forward failed")
  	}
  	return err
  }
docs: // Close closes the listener.