virtio-9p: add savem handlers

virtio-9p: add savem handlers

We don't support migration of mounted 9p shares. This is handled by a
migration blocker.

One would expect, however, to be able to migrate if the share is unmounted.
Unfortunately virtio-9p-device does not register savevm handlers at all !
Migration succeeds and leaves the guest with a dangling device...

This patch simply registers migration handlers for virtio-9p-device. Whether
migration is possible or not still depends on the migration blocker.

Signed-off-by: Greg Kurz <[email protected]>
Reviewed-by: Michael S. Tsirkin <[email protected]>
Signed-off-by: Michael S. Tsirkin <[email protected]>