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/net/ipv6/xfrm6_mode_tunnel.c b/net/ipv6/xfrm6_mode_tunnel.c
index 645cb96..4d6edff 100644
--- a/net/ipv6/xfrm6_mode_tunnel.c
+++ b/net/ipv6/xfrm6_mode_tunnel.c
@@ -20,7 +20,7 @@
 
 static inline void ipip6_ecn_decapsulate(struct sk_buff *skb)
 {
-	struct ipv6hdr *outer_iph = ipv6_hdr(skb);
+	const struct ipv6hdr *outer_iph = ipv6_hdr(skb);
 	struct ipv6hdr *inner_iph = ipipv6_hdr(skb);
 
 	if (INET_ECN_is_ce(ipv6_get_dsfield(outer_iph)))
@@ -55,8 +55,8 @@
 		dsfield &= ~INET_ECN_MASK;
 	ipv6_change_dsfield(top_iph, 0, dsfield);
 	top_iph->hop_limit = ip6_dst_hoplimit(dst->child);
-	ipv6_addr_copy(&top_iph->saddr, (struct in6_addr *)&x->props.saddr);
-	ipv6_addr_copy(&top_iph->daddr, (struct in6_addr *)&x->id.daddr);
+	ipv6_addr_copy(&top_iph->saddr, (const struct in6_addr *)&x->props.saddr);
+	ipv6_addr_copy(&top_iph->daddr, (const struct in6_addr *)&x->id.daddr);
 	return 0;
 }