MBUFQ_NEXT
m0 != MBUFQ_NEXT(m);
m = MBUFQ_NEXT(m);
m = MBUFQ_NEXT(m)) {
_m = m, m = MBUFQ_NEXT(m)) {
m0 != MBUFQ_NEXT(m);
m = MBUFQ_NEXT(m);
m = MBUFQ_NEXT(m)) {
_m = m, m = MBUFQ_NEXT(m)) {
m = MBUFQ_NEXT(m);