Multus default network feature requires the pod's default network annotation - `v1.multus-cni.io/default-network` to feature the namespace and NAD metadata name of the default network NAD.

We need configurable, since OpenShift, upstream (and potentially other CNIs that implement the `IPAMClaim` CRD feature of persistent IPs) use different namespaces to hold the default network NAD.

The suggested approach is to add a configuration knob to IPAMExtensions controller to override the namespace to look for this NAD.

In OpenShift Virt, HCO / CNAO will template this value accordingly.

If a simpler alternative can be found that allows the requirement, we could discuss them.