This patch has been successfully tested. Boot up a VM with a
virtio-mem device, hotplug some memory increasing the requested-size,
finally try to unplug the device and see the new message:
(qemu) device_del vmem0
Error: virtio-mem device cannot get unplugged while some of its memory
is still plugge
The error message is actually expressive, considering QEMU only. But
when called from Libvirt, talking about "size" can be confusing, because
in Libvirt "size" translates to the memory backend size in QEMU (maximum
size) and "current" translates to the QEMU "size" property.
Let's simply avoid talk
