nbd: Remove redundant sock->ops->shutdown() check in nbd_get_socket().

Since commit 9f7c02e ("nbd: restrict sockets to TCP
and UDP") (s/UDP/AF_UNIX/), NBD only accepts TCP and AF_UNIX
SOCK_STREAM sockets as backend.

nbd_get_socket() currently checks if sock->ops->shutdown()
is sock_no_shutdown(), but sock->ops->shutdown() is always
inet_shutdown() or unix_shutdown() for these socket types.

Let's remove the redundant check.

Signed-off-by: Kuniyuki Iwashima <[email protected]>

Author: q2ven

drivers/block/nbd.c

@@ -1228,13 +1228,6 @@ static struct socket *nbd_get_socket(struct nbd_device *nbd, unsigned long fd,
 		return NULL;
 	}
 
-	if (sock->ops->shutdown == sock_no_shutdown) {
-		dev_err(disk_to_dev(nbd->disk), "Unsupported socket: shutdown callout must be supported.\n");
-		*err = -EINVAL;
-		sockfd_put(sock);
-		return NULL;
-	}
-
 	return sock;
 }