IGB_TX_RESERVED
if (txr->tx_avail > IGB_MAX_SCATTER + IGB_TX_RESERVED) {
maxsegs = txr->tx_avail - IGB_TX_RESERVED;
if (txr->tx_avail <= IGB_MAX_SCATTER + IGB_TX_RESERVED) {
if (nsegs >= txr->num_tx_desc - IGB_MAX_SCATTER - IGB_TX_RESERVED) {