vmm: Fix virtio-rng creation with virtual IOMMU

If the virtio-rng device is supposed to be placed behind the virtual
IOMMU, this must be explicitly propagated through the code.

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

vmm/src/device_manager.rs

@@ -1421,7 +1421,7 @@ impl DeviceManager {
             ));
             devices.push((
                 Arc::clone(&virtio_rng_device) as VirtioDeviceArc,
-                false,
+                rng_config.iommu,
                 None,
             ));