When is VIRTIO_CONFIG_S_DRIVER_OK set?
I've seen in vhost-scsi from qemu, that it sets it's own set_status()
member function for a virtio object, which checks for
VIRTIO_CONFIG_S_DRIVER_OK (from a status variable received as a
parameter) so it knows if it has to call vhost_scsi_start(),
vhost_scsi_stop(), or don't do anything if the status already
corresponds to what was received.
I've tried to implement the same logic in my virtio device, but it
always triggers set_status() with a status of 0 (no flags set).
