MQ_PQRESQ
TAILQ_FOREACH(mit, &mq->mq_head[MQ_PQRESQ], msg_queue) {
TAILQ_INSERT_TAIL(&mq->mq_head[MQ_PQRESQ], msg, msg_queue);
msg = TAILQ_FIRST(&mq->mq_head[MQ_PQRESQ]);
idx = MQ_PQRESQ;
KASSERT(idx != MQ_PQRESQ);