in6p_cksum
int in6p_cksum; /* IPV6_CHECKSUM setsockopt */
#define in6p_cksum(inpcb) (((struct in6pcb *)(inpcb))->in6p_cksum)
in6p_cksum(inp) = optval;
optval = in6p_cksum(inp);
if (in6p_cksum(inp) != -1) {
m->m_pkthdr.len - *offp - 2 < in6p_cksum(inp) ||
in6p_cksum(inp) != -1) {
off = in6p_cksum(inp);
in6p_cksum(inp) = -1;
inp6->in6p_cksum = -1; /* just to be sure */
in6p_cksum(inp) = -1; /* just to be sure */