vdpa net: allow VHOST_F_LOG_ALL

vdpa net: allow VHOST_F_LOG_ALL

Since some actions move to the start function instead of init, the
device features may not be the parent vdpa device's, but the one
returned by vhost backend.  If transition to SVQ is supported, the vhost
backend will return _F_LOG_ALL to signal the device is migratable.

Add VHOST_F_LOG_ALL.  HW dirty page tracking can be added on top of this
change if the device supports it in the future.

Signed-off-by: Eugenio Pérez <eperezma@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20230303172445.1089785-14-eperezma@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>