nbd: error out if socket index doesn't match in nbd_handle_reply()

nbd: error out if socket index doesn't match in nbd_handle_reply()

commit fcf3d633d8e1 ("nbd: check sock index in nbd_read_stat()") just
add error message when socket index doesn't match. Since the request
and reply must be transmitted over the same socket, it's ok to error
out in such situation.

Signed-off-by: Yu Kuai <yukuai3@huawei.com>
Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Link: https://lore.kernel.org/r/20211101092538.1155842-1-yukuai3@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>