FR_IP_OFF
if (FR_IP_OFF(frea) > off)
FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) - frep->fr_ip->ip_hl *
precut = FR_IP_OFF(frep) + ntohs(frep->fr_ip->ip_len) -
for (; frea != NULL && ip_len + off > FR_IP_OFF(frea);
aftercut = ip_len + off - FR_IP_OFF(frea);
(next == NULL || FR_IP_OFF(next) != off))
off, next == NULL ? -1 : FR_IP_OFF(next),