inet_diag: constify raw_lookup() socket argument

Now both raw_v4_match() and raw_v6_match() accept a const socket,
raw_lookup() can do the same to clarify its role.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/raw_diag.c

@@ -34,7 +34,7 @@ raw_get_hashinfo(const struct inet_diag_req_v2 *r)
  * use helper to figure it out.
  */
 
-static bool raw_lookup(struct net *net, struct sock *sk,
+static bool raw_lookup(struct net *net, const struct sock *sk,
 		       const struct inet_diag_req_v2 *req)
 {
 	struct inet_diag_req_raw *r = (void *)req;