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/esp6.c b/net/ipv6/esp6.c
index 5aa8ec8..e97b4b7 100644
--- a/net/ipv6/esp6.c
+++ b/net/ipv6/esp6.c
@@ -430,7 +430,7 @@
 		     u8 type, u8 code, int offset, __be32 info)
 {
 	struct net *net = dev_net(skb->dev);
-	struct ipv6hdr *iph = (struct ipv6hdr*)skb->data;
+	const struct ipv6hdr *iph = (const struct ipv6hdr *)skb->data;
 	struct ip_esp_hdr *esph = (struct ip_esp_hdr *)(skb->data + offset);
 	struct xfrm_state *x;
 
@@ -438,7 +438,8 @@
 	    type != ICMPV6_PKT_TOOBIG)
 		return;
 
-	x = xfrm_state_lookup(net, skb->mark, (xfrm_address_t *)&iph->daddr, esph->spi, IPPROTO_ESP, AF_INET6);
+	x = xfrm_state_lookup(net, skb->mark, (const xfrm_address_t *)&iph->daddr,
+			      esph->spi, IPPROTO_ESP, AF_INET6);
 	if (!x)
 		return;
 	printk(KERN_DEBUG "pmtu discovery on SA ESP/%08x/%pI6\n",