USABLE_TX_BD_ALLOC
bce_dump_tx_mbuf_chain(sc, 0, USABLE_TX_BD_ALLOC);
bce_dump_tx_chain(sc, 0, USABLE_TX_BD_ALLOC);
if_setsendqlen(ifp, USABLE_TX_BD_ALLOC);
sc->max_tx_bd = USABLE_TX_BD_ALLOC;