virtio-net: get rid of unnecessary container of rq stats

We don't maintain tx counters in rx stats any more. There's no need
for an extra container of rq stats.

Cc: Toshiaki Makita <makita.toshiaki@lab.ntt.co.jp>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>