A lot of current code in network stack expects mbufs not having

m_nextpkt pointer, assuming that if there is one, then this is
a packet batch. Thus, mbufq_dequeue() needs to clear it on mbuf
that is being returned.

sys/sys/mbuf.h

@@ -1282,6 +1282,7 @@ mbufq_dequeue(struct mbufq *mq)
 	m = STAILQ_FIRST(&mq->mq_head);
 	if (m) {
 		STAILQ_REMOVE_HEAD(&mq->mq_head, m_stailqpkt);
+		m->m_nextpkt = NULL;
 		mq->mq_len--;
 	}
 	return (m);