virtio-gpu: block both 2d and 3d rendering

virtio-gpu: block both 2d and 3d rendering

Now that 2d commands are translated to 3d rendering, qemu must stop
sending 3d updates (from 2d) to Spice as well.

Fixes:
https://bugzilla.redhat.com/show_bug.cgi?id=1674324

Cc: cfergeau@redhat.com
Signed-off-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Reviewed-by: Christophe Fergeau <cfergeau@redhat.com>
Tested-by: Christophe Fergeau <cfergeau@redhat.com>
Message-id: 20190221114330.17968-4-marcandre.lureau@redhat.com
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>