commit bc505f37 upstream.

As all virtio devices perform DMA, we
must enable bus mastering for them to be
spec compliant.

This patch fixes hotplug of virtio devices
with Linux guests and qemu 0.11-0.12.
Tested-by: Alexander Graf <agraf@suse.de>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Cc: maximilian attems <max@stro.at>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>