XMT_HEADER_LEN
len += XMT_HEADER_LEN + 1;
len += XMT_HEADER_LEN;
if (avail >= len + XMT_HEADER_LEN) {
XMT_HEADER_LEN) {
sc->tx_tail = sc->tx_head + XMT_HEADER_LEN + (count + 1) * 6;