DEF_MRU
bundle->iface->mtu = DEF_MRU;
mru = DEF_MRU;
if (mru < DEF_MRU) {
lcp->his_mru = DEF_MRU;
lcp->want_mru = DEF_MRU;
u_char msg[DEF_MRU - 3];
char ident[DEF_MRU - 7]; /* SendIdentification() data */