x25: preserve const qualifier in [a]x25_sk()

We can change [a]x25_sk() to propagate their argument const qualifier,
thanks to container_of_const().
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>

include/net/ax25.h

@@ -260,10 +260,7 @@ struct ax25_sock {
 	struct ax25_cb		*cb;
 };
 
-static inline struct ax25_sock *ax25_sk(const struct sock *sk)
-{
-	return (struct ax25_sock *) sk;
-}
+#define ax25_sk(ptr) container_of_const(ptr, struct ax25_sock, sk)
 
 static inline struct ax25_cb *sk_to_ax25(const struct sock *sk)
 {

include/net/x25.h

@@ -177,10 +177,7 @@ struct x25_forward {
 	atomic_t		refcnt;
 };
 
-static inline struct x25_sock *x25_sk(const struct sock *sk)
-{
-	return (struct x25_sock *)sk;
-}
+#define x25_sk(ptr) container_of_const(ptr, struct x25_sock, sk)
 
 /* af_x25.c */
 extern int  sysctl_x25_restart_request_timeout;