inet: constify ip headers and in6_addr

Add const qualifiers to structs iphdr, ipv6hdr and in6_addr pointers
where possible, to make code intention more obvious.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/ndisc.h b/include/net/ndisc.h
index e0e594f..6144685 100644
--- a/include/net/ndisc.h
+++ b/include/net/ndisc.h
@@ -102,7 +102,8 @@
 						    struct neighbour *neigh,
 						    const struct in6_addr *target);
 
-extern int			ndisc_mc_map(struct in6_addr *addr, char *buf, struct net_device *dev, int dir);
+extern int			ndisc_mc_map(const struct in6_addr *addr, char *buf,
+					     struct net_device *dev, int dir);
 
 extern struct sk_buff		*ndisc_build_skb(struct net_device *dev,
 						 const struct in6_addr *daddr,