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>

net/ipv6/ip6mr.c

@@ -989,8 +989,8 @@ static int mif6_add(struct net *net, struct mr6_table *mrt,
 }
 
 static struct mfc6_cache *ip6mr_cache_find(struct mr6_table *mrt,
-					   struct in6_addr *origin,
-					   struct in6_addr *mcastgrp)
+					   const struct in6_addr *origin,
+					   const struct in6_addr *mcastgrp)
 {
 	int line = MFC6_HASH(mcastgrp, origin);
 	struct mfc6_cache *c;