npf_fixup16_cksum
cksum = npf_fixup16_cksum(cksum, old_port, port);
cksum = npf_fixup16_cksum(cksum, ipcksum, eip->ip_sum);
cksum = npf_fixup16_cksum(cksum, l4cksum, th->th_sum);
cksum = npf_fixup16_cksum(cksum, l4cksum, uh->uh_sum);
cksum = npf_fixup16_cksum(cksum, oid, nid);
cksum = npf_fixup16_cksum(cksum, ip_off, nip_off);
cksum = npf_fixup16_cksum(cksum, ttl, minttl);
cksum = npf_fixup16_cksum(cksum, old[0], new[0]);
cksum = npf_fixup16_cksum(cksum, old[1], new[1]);
cksum = npf_fixup16_cksum(th->th_sum, mss, maxmss);
uint16_t npf_fixup16_cksum(uint16_t, uint16_t, uint16_t);
cksum = npf_fixup16_cksum(cksum, oport, port);