add regression fix for migration with virtio-rng device

add regression fix for migration with virtio-rng device

between QEMU less than 7.2 and QEMU 7.2 without the fix (both
directions are affected).

As mentioned in the patch message, this fix itself will break
migration between QEMU 7.2 and QEMU 7.2 with the fix (in both
directions, if a virtio-rng device is attached), but this is fine,
because no pve-qemu-kvm package with QEMU 7.2 has been publicly
released yet.

Signed-off-by: Fiona Ebner <f.ebner@proxmox.com>