RX_NEXT
for (i = sc->rx.cur; ; i = RX_NEXT(i)) {
for (index = sc->rx.cur; ; index = RX_NEXT(index)) {
htole32(sc->rx.desc_ring_paddr + DESC_OFF(RX_NEXT(i)));
index = RX_NEXT(index, q->nentries);
sc->rx.head = RX_NEXT(sc->rx.head);