RX_QUEUE_MASK
i = (i + 1) & RX_QUEUE_MASK;
rxq->write = (rxq->write + 1) & RX_QUEUE_MASK;
rxq->write = (rxq->write + 1) & RX_QUEUE_MASK;
i = (i + 1) & RX_QUEUE_MASK;
rxq->write = (rxq->write + 1) & RX_QUEUE_MASK;
i = (i + 1) & RX_QUEUE_MASK, j++) {
num_rbs = (num_rbs - rxq->read) & RX_QUEUE_MASK;