[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/include/net/ipv6.h b/include/net/ipv6.h
index a0c285b..49c4898 100644
--- a/include/net/ipv6.h
+++ b/include/net/ipv6.h
@@ -451,8 +451,8 @@
 extern 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);
 
 extern int			ip6_find_1stfragopt(struct sk_buff *skb, u8 **nexthdr);