vdpa: move vhost_vdpa_set_vring_ready to the caller

vdpa: move vhost_vdpa_set_vring_ready to the caller

Doing that way allows CVQ to be enabled before the dataplane vqs,
restoring the state as MQ or MAC addresses properly in the case of a
migration.

The patch does it by defining a ->load NetClientInfo callback also for
dataplane.  Ideally, this should be done by an independent patch, but
the function is already static so it would only add an empty
vhost_vdpa_net_data_load stub.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Message-Id: <20230822085330.3978829-5-eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Tested-by: Lei Yang <leiyang@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>