ip_hdr_sanity_check
if ((l = ip_hdr_sanity_check(&ip_hdr, len)) == -1)
int ip_hdr_sanity_check(const struct ip *, u_int16_t);
if ((l = ip_hdr_sanity_check(&ip_hdr, len)) == -1)
int ip_hdr_sanity_check(const struct ip *, u_int16_t);