fr_makefrip
if (fr_makefrip(hlen, ip, fin) == -1) {
(void) fr_makefrip(hlen, ip, &fnew);
(void) fr_makefrip(IP_HL(oip) << 2, oip, &ofin);
(void) fr_makefrip(sizeof(*oip6), (ip_t *)oip6, &ofin);
extern int fr_makefrip __P((int, ip_t *, fr_info_t *));