This will confuse driver if migrating during initialization. Solves
this issue by:
- introduce transport specific callbacks to load and store extra
virtqueue states.
- add a new subsection for virtio to migrate transport specific modern
device state.
- implement pci specific callbacks.
- add a new property for virtio-pci for whether or not to migrate
extra state.
- compat the migration for 2.4 and elder machine types
Cc: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Jason Wang <jasowang@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com> Reviewed-by: Cornelia Huck <cornelia.huck@de.ibm.com>