PPP_FCSLEN
#define PPP_MAXMTU 65535 - (PPP_HDRLEN + PPP_FCSLEN)
if (++sc->sc_ilen > sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN) {
for (len = sc->sc_mru + PPP_HDRLEN + PPP_FCSLEN; len > 0; ){
if (ilen < PPP_HDRLEN + PPP_FCSLEN) {