[IPV6]: Make address arguments const.

- net/ipv6/addrconf.c:
	ipv6_get_ifaddr(), ipv6_dev_get_saddr()
- net/ipv6/mcast.c:
	ipv6_sock_mc_join(), ipv6_sock_mc_drop(),
	inet6_mc_check(),
	ipv6_dev_mc_inc(), __ipv6_dev_mc_dec(), ipv6_dev_mc_dec(),
	ipv6_chk_mcast_addr()
- net/ipv6/route.c:
	rt6_lookup(), icmp6_dst_alloc()
- net/ipv6/ip6_output.c:
	ip6_nd_hdr()
- net/ipv6/ndisc.c:
	ndisc_send_ns(), ndisc_send_rs(), ndisc_send_redirect(),
	ndisc_get_neigh(), __ndisc_send()

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
diff --git a/net/ipv6/ip6_output.c b/net/ipv6/ip6_output.c
index c0dbe54..0af2e05 100644
--- a/net/ipv6/ip6_output.c
+++ b/net/ipv6/ip6_output.c
@@ -286,7 +286,7 @@
  */
 
 int ip6_nd_hdr(struct sock *sk, struct sk_buff *skb, struct net_device *dev,
-	       struct in6_addr *saddr, struct in6_addr *daddr,
+	       const struct in6_addr *saddr, const struct in6_addr *daddr,
 	       int proto, int len)
 {
 	struct ipv6_pinfo *np = inet6_sk(sk);