What would you like to be added:

Ive done preliminary testing with agnhost on calico powered clusters on some windows variants and found that the probing seems to work.

Can we add

ginkgo.Describe("sig-windows")... 
  nodeSelector:
    kubernetes.io/os: windows

wrapper to netpol suite so that we can run it on windows clusters @mattfenwick ?

Why is this needed:

We need this because otherwise, CNIs such as EKS will give us

I0106 03:14:48.618196       1 webhook.go:245] Skipping mutation for netpol-6932-z/b due to policy check.
I0106 03:14:48.802101       1 webhook.go:241] AdmissionReview for Kind=/v1, Kind=Pod, Namespace=netpol-6932-z Name=c (c) UID=465ac7ac-ad7e-4327-b0d0-480d580c630c PatchOperation=CREATE UserInfo={kubernetes-admin heptio-authenticator-aws:192930162896:AIDASZ24IVDIN76ZW4WDA [system:masters system:authenticated] map[accessKeyId:[AKIASZ24IVDIFXUIP5PB]]}.
I0106 03:14:48.802132       1 webhook.go:289] Skip mutation for c as the target platform is .
I0106 03:14:48.802139       1 webhook.go:245] Skipping mutation for netpol-6932-z/c due to policy check.

This error is caused when, for example, pods that are landing on a windows node havent defined their target platform. Somehow i guess pods which are landing on linux nodes dont have this issue.

Its also needed for the obvious reason that we probably want separate linux and windows test suites for policies, in general, even though we expect the logic to be identical (modulo hostports , which we dont currently test)