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/dccp/ipv6.c b/net/dccp/ipv6.c
index de1b7e3..73add23 100644
--- a/net/dccp/ipv6.c
+++ b/net/dccp/ipv6.c
@@ -54,8 +54,8 @@
 
 /* add pseudo-header to DCCP checksum stored in skb->csum */
 static inline __sum16 dccp_v6_csum_finish(struct sk_buff *skb,
-				      struct in6_addr *saddr,
-				      struct in6_addr *daddr)
+				      const struct in6_addr *saddr,
+				      const struct in6_addr *daddr)
 {
 	return csum_ipv6_magic(saddr, daddr, skb->len, IPPROTO_DCCP, skb->csum);
 }
@@ -87,7 +87,7 @@
 static void dccp_v6_err(struct sk_buff *skb, struct inet6_skb_parm *opt,
 			u8 type, u8 code, int offset, __be32 info)
 {
-	struct ipv6hdr *hdr = (struct ipv6hdr *)skb->data;
+	const struct ipv6hdr *hdr = (const struct ipv6hdr *)skb->data;
 	const struct dccp_hdr *dh = (struct dccp_hdr *)(skb->data + offset);
 	struct dccp_sock *dp;
 	struct ipv6_pinfo *np;
@@ -296,7 +296,7 @@
 
 static void dccp_v6_ctl_send_reset(struct sock *sk, struct sk_buff *rxskb)
 {
-	struct ipv6hdr *rxip6h;
+	const struct ipv6hdr *rxip6h;
 	struct sk_buff *skb;
 	struct flowi6 fl6;
 	struct net *net = dev_net(skb_dst(rxskb)->dev);