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Test Proxy Mode

**What this PR does / why we need it**:

Currently, IPVS-based kube-proxy is protected by feature gateway and there is no UT for it. We should test ipvs proxy mode when feature gateway is set.

**Which issue(s) this PR fixes**:
Fixes #56404

**Special notes for your reviewer**:

**Release note**:

```release-note
NONE
```