virtio-devices: mem: Allow for an initial size

This commit gives the possibility to create a virtio-mem device with
some memory already plugged into it. This is preliminary work to be
able to reboot a VM with the virtio-mem region being already resized.

Signed-off-by: Hui Zhu <teawater@antfin.com>
Signed-off-by: Sebastien Boeuf <sebastien.boeuf@intel.com>

vmm/src/device_manager.rs

@@ -2451,6 +2451,7 @@ impl DeviceManager {
                             .map_err(DeviceManagerError::TryCloneVirtioMemResize)?,
                         self.seccomp_action.clone(),
                         node_id,
+                        0,
                     )
                     .map_err(DeviceManagerError::CreateVirtioMem)?,
                 ));