This patch introduces a boolean for the device has control queue which
can accepts control command via network queue.

The first user would be the control virtqueue support for vhost.

Signed-off-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20211020045600.16082-6-jasowang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>