TBSShift
np->cur_tx_copy->control |= (skb->len << TBSShift); /* buffer size */
np->cur_tx_copy->control |= (BPT << TBSShift); /* buffer size */
next->control |= ((skb->len - BPT) << TBSShift); /* buf size */
np->cur_tx_copy->control |= (skb->len << TBSShift); /* buffer size */