Merge remote-tracking branch 'mst/tags/for_anthony' into staging

* mst/tags/for_anthony:
  virtio-serial-bus: let chardev know the exact number of bytes requested
  virtio: Introduce virtqueue_get_avail_bytes()
  virtio: use unsigned int for counting bytes in vq
  iov: add const annotation
  virtio-net: fix used len for tx
  virtio: don't mark unaccessed memory as dirty