igc_rxdesc_incr
const int start = igc_rxdesc_incr(sc, rxr->last_desc_filled);
for (id = start; id != rxr->next_to_check; id = igc_rxdesc_incr(sc, id)) {
int nextp = igc_rxdesc_incr(sc, id);
id = igc_rxdesc_incr(sc, id);