fix(vm): skip template network sync for main-only VMs

[LopatinDmitr]

Description

Skip the network template synchronization path for VirtualMachines that only use the implicit Main network.

The network hotplug reconciliation can detect a mismatch between the desired implicit default network and an existing KubeVirt VM template that does not explicitly contain spec.template.spec.domain.devices.interfaces / spec.template.spec.networks. For Main-only VMs this mismatch must not be reconciled into a running KubeVirt VM template, because materializing the implicit default network as an explicit template field creates a non-live-updatable diff for KubeVirt.

Why do we need it, and what problem does it solve?

After the network hotplug changes, SyncKvvmHandler can enter the networksOutOfSync -> applyNetworkReadinessSync -> updateKVVM path for a Main-only VM.

For such VMs, the running VMI already has the default pod network via KubeVirt defaulting, but the KubeVirt VM template may not explicitly contain it. Updating the template while the VM is running changes:

spec.template.spec.domain.devices.interfaces:
- name: default
  bridge: {}
  model: virtio
  acpiIndex: 1

spec.template.spec.networks:
- name: default
  pod: {}

Older virt-controller versions can see this [] -> [default] template diff during module rollout and set KubeVirt RestartRequired=True with a non-live-updatable field was changed in the template spec. DVP then exposes it as AwaitingRestartToApplyConfiguration=True with UnexpectedState.

The same path can also produce a misleading ConfigurationApplied=False message about waiting for SDN, even though Main-only VMs do not have additional SDN-managed interfaces to wait for.

This fix skips the out-of-sync network reconciliation and readiness/update path for Main-only VMs. VMs with additional networks still use the existing SDN readiness and hotplug flow.

What is the expected result?

1. Create a VM without explicit spec.networks or with only the Main network.
2. Roll out the virtualization module version that contains network hotplug changes.
3. Verify that the VM does not get:
   • ConfigurationApplied=False with Waiting for SDN to configure network interfaces on the pod.
   • AwaitingRestartToApplyConfiguration=True caused by materializing the implicit default network in the KubeVirt VM template.
4. Verify that VMs with additional networks still reconcile through the SDN readiness path.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: fix
summary: Prevent Main-only virtual machines from requiring restart due to implicit default network template synchronization.