udp: preserve const qualifier in udp_sk()

We can change udp_sk() to propagate const qualifier of its argument,
thanks to container_of_const()

This should avoid some potential errors caused by accidental
(const -> not_const) promotion.

Signed-off-by: Eric Dumazet <[e-mail]>
Cc: Willem de Bruijn <[e-mail]>
Reviewed-by: Simon Horman <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

include/linux/udp.h

···
 
 #define UDP_MAX_SEGMENTS	(1 << 6UL)
 
-static inline struct udp_sock *udp_sk(const struct sock *sk)
-{
-	return (struct udp_sock *)sk;
-}
+#define udp_sk(ptr) container_of_const(ptr, struct udp_sock, inet.sk)
 
 static inline void udp_set_no_check6_tx(struct sock *sk, bool val)
 {