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