nbd_config is allocated in nbd_alloc_config(), but never freed.
Fixes: 2bc063dc9d47 ("nbd: separate out the config information") Signed-off-by: Ilya Dryomov <idryomov@gmail.com> Reviewed-by: Josef Bacik <jbacik@fb.com> Signed-off-by: Jens Axboe <axboe@fb.com>