Now that bdrv_graph_wrlock() temporarily drops the AioContext lock that
its caller holds, it can poll without causing deadlocks. We can now
re-enable graph locking.

This reverts commit ad128dff0bf4b6f971d05eb4335a627883a19c1d.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Message-ID: <20230605085711.21261-12-kwolf@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>