ipf_fix_incksum
ipf_fix_incksum(0, &icmp->icmp_cksum, sumd2, 0);
ipf_fix_incksum(fin->fin_cksum & FI_CK_L4PART,
ipf_fix_incksum(fin->fin_cksum, csump,
ipf_fix_incksum(0, &fin->fin_ip->ip_sum, ipsumd, 0);
ipf_fix_incksum(0, csump, nat->nat_sumd[0], 0);
extern void ipf_fix_incksum(int, u_short *, u_32_t, u_32_t);
ipf_fix_incksum(0, &icmp6->icmp6_cksum,
ipf_fix_incksum(fin->fin_cksum, csump,
ipf_fix_incksum(0, csump, nat->nat_sumd[0], 0);
ipf_fix_incksum(0, &tcp->th_sum, is->is_sumd[0], 0);
ipf_fix_incksum(0, &tcp->th_sum, is->is_sumd[1], 0);