IWI_TX_RING_COUNT
txq->next = (txq->next + 1) % IWI_TX_RING_COUNT;
txq->cur = (txq->cur + 1) % IWI_TX_RING_COUNT;
if (sc->txq[ac].queued > IWI_TX_RING_COUNT - 8) {
error = iwi_alloc_tx_ring(sc, &sc->txq[i], IWI_TX_RING_COUNT,