vhost: rework IOTLB messaging

This patch reworks IOTLB messaging to prepare for vhost-user
device IOTLB support.

IOTLB messages handling is extracted from vhost-kernel backend,
so that only the messages transport remains backend specifics.

Signed-off-by: Maxime Coquelin <maxime.coquelin@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
3 files changed