Currently, the VMI controller instantiate the network admitter as part of its sync flow [1].

Decouple it from the VMI controller and add a unit test to make sure its being called.

 [1]https://github.com/kubevirt/kubevirt/blob/4a882259231e0f81be7d064d64262af284fa7759/pkg/virt-controller/watch/vmi/vmi.go#L1024