nd_opt_dnssl
struct nd_opt_dnssl *ndopt_dnssl;
packlen += sizeof(struct nd_opt_dnssl);
ndopt_dnssl = (struct nd_opt_dnssl *)buf;
(optlen - sizeof(struct nd_opt_dnssl)) % 8 == 0)
struct nd_opt_dnssl *dnssl;
dnssl = (struct nd_opt_dnssl *)raoptp;