smc: preserve const qualifier in smc_sk()

We can change smc_sk() to propagate its argument const qualifier,
thanks to container_of_const().

Signed-off-by: Eric Dumazet <[email protected]>
Cc: Karsten Graul <[email protected]>
Cc: Wenjia Zhang <[email protected]>
Cc: Jan Karcher <[email protected]>
Reviewed-by: Simon Horman <[email protected]>
Reviewed-by: Wenjia Zhang <[email protected]>
Signed-off-by: David S. Miller <[email protected]>

Author: edumazet

net/smc/smc.h

@@ -283,10 +283,7 @@ struct smc_sock {				/* smc sock container */
 						 * */
 };
 
-static inline struct smc_sock *smc_sk(const struct sock *sk)
-{
-	return (struct smc_sock *)sk;
-}
+#define smc_sk(ptr) container_of_const(ptr, struct smc_sock, sk)
 
 static inline void smc_init_saved_callbacks(struct smc_sock *smc)
 {