radv: Fix RFC reference in comments

  list rdnss_list;		/* Local list of RDNSS configs (struct radv_rdnss_config) */

  list dnssl_list;		/* Local list of DNSSL configs (struct radv_dnssl_config) */

  u32 min_ra_int;		/* Standard options from RFC 4261 */

  u32 min_ra_int;		/* Standard options from RFC 4861 */

  u32 max_ra_int;

  u32 min_delay;

  u8 rdnss_local;		/* Global list is not used for RDNSS */

  u8 dnssl_local;		/* Global list is not used for DNSSL */

  u8 managed;			/* Standard options from RFC 4261 */

  u8 managed;			/* Standard options from RFC 4861 */

  u8 other_config;

  u32 link_mtu;

  u32 reachable_time;

  uint pxlen;

  u8 skip;			/* Do not include this prefix to RA */

  u8 onlink;			/* Standard options from RFC 4261 */

  u8 onlink;			/* Standard options from RFC 4861 */

  u8 autonomous;

  u32 valid_lifetime;

  u32 preferred_lifetime;