vmm: Add hotplugged_size to VirtioMemZone

Adding a new field to VirtioMemZone structure, as it lets us associate
with a particular virtio-mem region the amount of memory that should be
plugged in at boot.

Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/device_manager.rs

@@ -2449,7 +2449,7 @@ impl DeviceManager {
                             .map_err(DeviceManagerError::TryCloneVirtioMemResize)?,
                         self.seccomp_action.clone(),
                         node_id,
-                        0,
+                        virtio_mem_zone.hotplugged_size(),
                     )
                     .map_err(DeviceManagerError::CreateVirtioMem)?,
                 ));