vDPA: check VIRTIO_NET_F_RSS for max_virtqueue_paris's presence

virtio 1.2 spec says:
max_virtqueue_pairs only exists if VIRTIO_NET_F_MQ or
VIRTIO_NET_F_RSS is set.

So when reporint MQ to userspace, it should check both
VIRTIO_NET_F_MQ and VIRTIO_NET_F_RSS.

unused parameter struct vdpa_device *vdev is removed

Signed-off-by: Zhu Lingshan <lingshan.zhu@intel.com>
Acked-by: Jason Wang <jasowang@redhat.com>
Message-Id: <20220929014555.112323-4-lingshan.zhu@intel.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>