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/syncookies.c b/net/ipv6/syncookies.c
index 352c260..8b9644a 100644
--- a/net/ipv6/syncookies.c
+++ b/net/ipv6/syncookies.c
@@ -66,7 +66,7 @@
 static DEFINE_PER_CPU(__u32 [16 + 5 + SHA_WORKSPACE_WORDS],
 		      ipv6_cookie_scratch);
 
-static u32 cookie_hash(struct in6_addr *saddr, struct in6_addr *daddr,
+static u32 cookie_hash(const struct in6_addr *saddr, const struct in6_addr *daddr,
 		       __be16 sport, __be16 dport, u32 count, int c)
 {
 	__u32 *tmp = __get_cpu_var(ipv6_cookie_scratch);
@@ -86,7 +86,8 @@
 	return tmp[17];
 }
 
-static __u32 secure_tcp_syn_cookie(struct in6_addr *saddr, struct in6_addr *daddr,
+static __u32 secure_tcp_syn_cookie(const struct in6_addr *saddr,
+				   const struct in6_addr *daddr,
 				   __be16 sport, __be16 dport, __u32 sseq,
 				   __u32 count, __u32 data)
 {
@@ -96,8 +97,8 @@
 		& COOKIEMASK));
 }
 
-static __u32 check_tcp_syn_cookie(__u32 cookie, struct in6_addr *saddr,
-				  struct in6_addr *daddr, __be16 sport,
+static __u32 check_tcp_syn_cookie(__u32 cookie, const struct in6_addr *saddr,
+				  const struct in6_addr *daddr, __be16 sport,
 				  __be16 dport, __u32 sseq, __u32 count,
 				  __u32 maxdiff)
 {
@@ -116,7 +117,7 @@
 
 __u32 cookie_v6_init_sequence(struct sock *sk, struct sk_buff *skb, __u16 *mssp)
 {
-	struct ipv6hdr *iph = ipv6_hdr(skb);
+	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct tcphdr *th = tcp_hdr(skb);
 	int mssind;
 	const __u16 mss = *mssp;
@@ -138,7 +139,7 @@
 
 static inline int cookie_check(struct sk_buff *skb, __u32 cookie)
 {
-	struct ipv6hdr *iph = ipv6_hdr(skb);
+	const struct ipv6hdr *iph = ipv6_hdr(skb);
 	const struct tcphdr *th = tcp_hdr(skb);
 	__u32 seq = ntohl(th->seq) - 1;
 	__u32 mssind = check_tcp_syn_cookie(cookie, &iph->saddr, &iph->daddr,