ND_OPT_DNSSL
ndopt_dnssl->nd_opt_dnssl_type = ND_OPT_DNSSL;
[ND_OPT_DNSSL] = NDOPT_FLAG_DNSSL,
hdr->nd_opt_type != ND_OPT_DNSSL)
(hdr->nd_opt_type == ND_OPT_DNSSL &&
case ND_OPT_DNSSL: