TX_HEADER_SIZE
pkt_size += TX_HEADER_SIZE;
if (((pkt_size + TX_HEADER_SIZE) & align_mask) == 0) {
pkt_size += TX_HEADER_SIZE;
if ((new = allocb(TX_HEADER_SIZE + pkt_size, 0)) == NULL) {
new->b_wptr = new->b_rptr + TX_HEADER_SIZE + pkt_size;
bp += TX_HEADER_SIZE;