Keep the NBD server always in the same AIO context as the exported BDS
by calling bdrv_add_aio_context_notifier() and implementing the required
callbacks.
Signed-off-by: NMax Reitz <mreitz@redhat.com>
Reviewed-by: NStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>