IPAddressFamily_cmp
if (IPAddressFamily_cmp(&a, &b) >= 0)
(void)sk_IPAddressFamily_set_cmp_func(addr, IPAddressFamily_cmp);
if ((addr = sk_IPAddressFamily_new(IPAddressFamily_cmp)) == NULL) {
(void)sk_IPAddressFamily_set_cmp_func(ext, IPAddressFamily_cmp);
(void)sk_IPAddressFamily_set_cmp_func(parent, IPAddressFamily_cmp);