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kube-proxy: fix field name comments & json tags
**What this PR does / why we need it**: correct some minor issues in the comments and json tags for some of the fields in the kube-proxy config structs.
**Which issue(s) this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close the issue(s) when PR gets merged)*:
Fixes #
**Special notes for your reviewer**:
**Release note**:
```release-note
The udpTimeoutMilliseconds field in the kube-proxy configuration file has been renamed to udpIdleTimeout. Action required: administrators need to update their files accordingly.
```
This was extracted from my currently unmerged f074b28fe9, as requested [here](https://github.com/kubernetes/kubernetes/pull/52198#pullrequestreview-85538637).
@kubernetes/sig-network-pr-reviews @luxas
When kube-proxy was refactored to use a configuration file, the ability
to use 0 for conntrack min, max, max per core, and tcp timeouts was
inadvertently broken; if you specified 0, it would instead apply the
default value from defaults.go.
This change restores the ability to use 0 to mean 0.
Signed-off-by: Andy Goldstein <andy.goldstein@gmail.com>