MVXPE_TX_MBUF
MVXPE_TX_MBUF(sc, q, i) = NULL;
m = MVXPE_TX_MBUF(sc, q, i);
MVXPE_TX_MBUF(sc, q, i) = NULL;
KASSERT(MVXPE_TX_MBUF(sc, q, tx->tx_cpu) == NULL);
MVXPE_TX_MBUF(sc, q, tx->tx_cpu) = m;
m = MVXPE_TX_MBUF(sc, q, tx->tx_dma);
MVXPE_TX_MBUF(sc, q, tx->tx_dma) = NULL;