mbq_dequeue
while ((m = mbq_dequeue(q)) != NULL) {
while ( nm_i != stop_i && (m = mbq_dequeue(q)) != NULL ) {
mbq_dequeue(&kring->rx_queue);
m = mbq_dequeue(&tmpq);
m = safe ? mbq_safe_dequeue(q) : mbq_dequeue(q);
struct mbuf *mbq_dequeue(struct mbq *q);