pi_AdvLinkMTU
if (pi->pi_AdvLinkMTU != 0) {
mo->nd_opt_mtu_mtu = htonl(pi->pi_AdvLinkMTU);
if (pi->pi_AdvLinkMTU != 0 &&
pi->pi_AdvLinkMTU != mtu) {
mtu, pi->pi_AdvLinkMTU);