tcp: md5: add more const attributes

Now tcp_md5_hash_header() has a const tcphdr argument, we can add more
const attributes to callers.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/tcp_ipv6.c

diff --git a/net/ipv6/tcp_ipv6.c b/net/ipv6/tcp_ipv6.c
index da2ada8..c8683fc 100644
--- a/net/ipv6/tcp_ipv6.c
+++ b/net/ipv6/tcp_ipv6.c
@@ -761,7 +761,7 @@
 
 static int tcp_v6_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,
 			       const struct in6_addr *daddr, struct in6_addr *saddr,
-			       struct tcphdr *th)
+			       const struct tcphdr *th)
 {
 	struct tcp_md5sig_pool *hp;
 	struct hash_desc *desc;
@@ -793,13 +793,14 @@
 }
 
 static int tcp_v6_md5_hash_skb(char *md5_hash, struct tcp_md5sig_key *key,
-			       struct sock *sk, struct request_sock *req,
-			       struct sk_buff *skb)
+			       const struct sock *sk,
+			       const struct request_sock *req,
+			       const struct sk_buff *skb)
 {
 	const struct in6_addr *saddr, *daddr;
 	struct tcp_md5sig_pool *hp;
 	struct hash_desc *desc;
-	struct tcphdr *th = tcp_hdr(skb);
+	const struct tcphdr *th = tcp_hdr(skb);
 
 	if (sk) {
 		saddr = &inet6_sk(sk)->saddr;
@@ -842,12 +843,12 @@
 	return 1;
 }
 
-static int tcp_v6_inbound_md5_hash (struct sock *sk, struct sk_buff *skb)
+static int tcp_v6_inbound_md5_hash(struct sock *sk, const struct sk_buff *skb)
 {
 	const __u8 *hash_location = NULL;
 	struct tcp_md5sig_key *hash_expected;
 	const struct ipv6hdr *ip6h = ipv6_hdr(skb);
-	struct tcphdr *th = tcp_hdr(skb);
+	const struct tcphdr *th = tcp_hdr(skb);
 	int genhash;
 	u8 newhash[16];