vdpa: Restore receive-side scaling state

This patch reuses vhost_vdpa_net_load_rss() with some
refactorings to restore the receive-side scaling state
at device's startup.

Signed-off-by: Hawkins Jiawei <yin31149@gmail.com>
Message-Id: <cf5b78a16ed0318982ceffb195f2227f6aad4ac1.1698195059.git.yin31149@gmail.com>
Acked-by: Eugenio Pérez <eperezma@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>