WM_NEXTTX
for (j = txs->txs_firstdesc; ; j = WM_NEXTTX(txq, j)) {
txq->txq_next = WM_NEXTTX(txq, txq->txq_next);
txq->txq_next = WM_NEXTTX(txq, txq->txq_next);
nexttx = WM_NEXTTX(txq, nexttx)) {
txq->txq_next = WM_NEXTTX(txq, txq->txq_next);
nexttx = WM_NEXTTX(txq, nexttx);
seg++, nexttx = WM_NEXTTX(txq, nexttx)) {