[IPV6]: Fixed the size of the netlink message notified by inet6_rt_notify().

I think the return value of rt6_nlmsg_size() should includes the
amount of RTA_METRICS.
Signed-off-by: Noriaki TAKAMIYA <takamiya@po.ntts.co.jp>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/route.c

@@ -2017,6 +2017,7 @@ static inline size_t rt6_nlmsg_size(void)
 	       + nla_total_size(4) /* RTA_IIF */
 	       + nla_total_size(4) /* RTA_OIF */
 	       + nla_total_size(4) /* RTA_PRIORITY */
+	       + RTAX_MAX * nla_total_size(4) /* RTA_METRICS */
 	       + nla_total_size(sizeof(struct rta_cacheinfo));
 }