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/inetpeer.h b/include/net/inetpeer.h
index e6dd8da6..8a159cc 100644
--- a/include/net/inetpeer.h
+++ b/include/net/inetpeer.h
@@ -80,7 +80,7 @@
 	return inet_getpeer(&daddr, create);
 }
 
-static inline struct inet_peer *inet_getpeer_v6(struct in6_addr *v6daddr, int create)
+static inline struct inet_peer *inet_getpeer_v6(const struct in6_addr *v6daddr, int create)
 {
 	struct inetpeer_addr daddr;