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>
diff --git a/net/ipv4/tcp_ipv4.c b/net/ipv4/tcp_ipv4.c
index 955c925..1dad7e9 100644
--- a/net/ipv4/tcp_ipv4.c
+++ b/net/ipv4/tcp_ipv4.c
@@ -92,7 +92,7 @@
 static struct tcp_md5sig_key *tcp_v4_md5_do_lookup(struct sock *sk,
 						   __be32 addr);
 static int tcp_v4_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,
-			       __be32 daddr, __be32 saddr, struct tcphdr *th);
+			       __be32 daddr, __be32 saddr, const struct tcphdr *th);
 #else
 static inline
 struct tcp_md5sig_key *tcp_v4_md5_do_lookup(struct sock *sk, __be32 addr)
@@ -1090,7 +1090,7 @@
 }
 
 static int tcp_v4_md5_hash_hdr(char *md5_hash, struct tcp_md5sig_key *key,
-			       __be32 daddr, __be32 saddr, struct tcphdr *th)
+			       __be32 daddr, __be32 saddr, const struct tcphdr *th)
 {
 	struct tcp_md5sig_pool *hp;
 	struct hash_desc *desc;
@@ -1122,12 +1122,12 @@
 }
 
 int tcp_v4_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)
 {
 	struct tcp_md5sig_pool *hp;
 	struct hash_desc *desc;
-	struct tcphdr *th = tcp_hdr(skb);
+	const struct tcphdr *th = tcp_hdr(skb);
 	__be32 saddr, daddr;
 
 	if (sk) {
@@ -1172,7 +1172,7 @@
 }
 EXPORT_SYMBOL(tcp_v4_md5_hash_skb);
 
-static int tcp_v4_inbound_md5_hash(struct sock *sk, struct sk_buff *skb)
+static int tcp_v4_inbound_md5_hash(struct sock *sk, const struct sk_buff *skb)
 {
 	/*
 	 * This gets called for each TCP segment that arrives