m_stailqpkt
n = STAILQ_NEXT(m, m_stailqpkt);
return (STAILQ_LAST(&mq->mq_head, mbuf, m_stailqpkt));
STAILQ_INSERT_TAIL(&mq->mq_head, m, m_stailqpkt);
STAILQ_REMOVE_HEAD(&mq->mq_head, m_stailqpkt);
STAILQ_INSERT_HEAD(&mq->mq_head, m, m_stailqpkt);