x25: Use sock_orphan() instead of open-coded (and buggy) variant.

It doesn't grab the sk_callback_lock, it doesn't NULL out
the sk->sk_sleep waitqueue pointer, etc.
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/x25/af_x25.c

@@ -612,8 +612,7 @@ static int x25_release(struct socket *sock)
 			break;
 	}
 
-	sock->sk	= NULL;
-	sk->sk_socket	= NULL;	/* Not used, but we should do this */
+	sock_orphan(sk);
 out:
 	return 0;
 }