socket ipv6编程，filter只接收icmpv6 ra rs报文

struct nd_router_advert       /* router advertisement */
  {
   
    struct icmp6_hdr  nd_ra_hdr;
    uint32_t   nd_ra_reachable;   /* reachable time */
    uint32_t   nd_ra_retransmit;  /* retransmit timer */
    /* could be followed by options */
  };
include/netinet/icmp6