carp_cksum
ch.carp_cksum = 0;
ch_ptr->carp_cksum = carp_cksum(m, len - sizeof(*ip));
ch_ptr->carp_cksum = carp_cksum(m, len - sizeof(*ip6));
if (carp_cksum(m, len - iplen)) {
if (carp_cksum(m, sizeof(*ch))) {
u_int16_t carp_cksum;