mac_get_mtu
trm_len = mac_get_mtu();
dhcp_buf_size = mac_get_mtu();
if ((ogp->igm_mp->b_wptr - ogp->igm_mp->b_rptr) > mac_get_mtu()) {
extern int mac_get_mtu(void);
tcp->tcp_if_mtu = mac_get_mtu() - 50;
tcp->tcp_if_mtu = mac_get_mtu();