ixgbe_legacy_tx_desc
sc->num_tx_desc * sizeof(struct ixgbe_legacy_tx_desc));
struct ixgbe_legacy_tx_desc *tx_desc;
tx_desc = (struct ixgbe_legacy_tx_desc *)&txr->tx_base[last];
sc->num_tx_desc * sizeof(struct ixgbe_legacy_tx_desc));