vdpa/snet: implement the resume vDPA callback

The callback sends a resume command to the DPU through
the control mechanism.

Signed-off-by: Alvaro Karsz <alvaro.karsz@solid-run.com>
Message-Id: <20230502131048.61134-1-alvaro.karsz@solid-run.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>