Description

Adds support for hotplugging and hotunplugging additional network interfaces (Network, ClusterNetwork) on running VMs without restart.

Changes

Comparator (pkg/controller/vmchange/comparator_pod_placement.go)

• compareNetworks now classifies non-Main network add/remove as ActionApplyImmediate instead of ActionRestart. Main network changes still require restart. New helper isOnlyNonMainNetworksChanged treats nil/empty spec.networks as equivalent to having an implicit default Main, so the nil → [Main, additional] transition is also non-disruptive.

Apply path (pkg/controller/vm/internal/sync_kvvm.go)

• For ActionApplyImmediate changes that touch networks, the controller now:

1. Patches the running pod's network.deckhouse.io/networks-spec annotation directly so the SDN module creates/removes the tap before KubeVirt tries to attach it (KVVM template annotation changes don't propagate to a running pod).
2. Waits for the SDN to report the interface as ready via network.deckhouse.io/networks-status (uses pod watcher to retrigger reconcile) — without this, virt-launcher panics with "Link not found" when libvirt tries to attach a tap that doesn't exist yet.
3. Updates the KVVM, which KubeVirt then syncs to the VMI; virt-handler hotplugs the interface via libvirt.

KVVM builder (pkg/controller/kvbuilder/kvvm.go, kvvm_utils.go)

• New SetNetworkInterfaceAbsent method sets State: virtv1.InterfaceStateAbsent on an interface to signal hotunplug to KubeVirt.

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

Currently, adding or removing additional networks on a VM requires a full restart, which is disruptive for production workloads. With this PR users can attach/detach Network/ClusterNetwork interfaces on running VMs and the changes take effect in the guest OS without reboot.

What is the expected result?

1. Create a VM with a Main network and wait for Running.
2. Patch spec.networks to add a ClusterNetwork. The VM's NeedRestart field stays clear; the new interface appears in the guest OS within seconds.
3. Patch spec.networks to remove the ClusterNetwork. The interface disappears from the guest OS without a restart.
4. Adding/removing a Main network still requires a restart (AwaitingRestartToApplyConfiguration condition is set).

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: feature
summary: support hotplug/hotunplug of additional network interfaces