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/ipv4/af_inet.c b/net/ipv4/af_inet.c
index 807d83c..cae75ef 100644
--- a/net/ipv4/af_inet.c
+++ b/net/ipv4/af_inet.c
@@ -1186,7 +1186,7 @@
 
 static int inet_gso_send_check(struct sk_buff *skb)
 {
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	const struct net_protocol *ops;
 	int proto;
 	int ihl;
@@ -1293,7 +1293,7 @@
 	const struct net_protocol *ops;
 	struct sk_buff **pp = NULL;
 	struct sk_buff *p;
-	struct iphdr *iph;
+	const struct iphdr *iph;
 	unsigned int hlen;
 	unsigned int off;
 	unsigned int id;