Ensure tcp6 and udp6 metrics are published via Prometheus

[hangongithub]

Fixes #2066

This is a duplicate of: #2084

It somehow got closed when I updated my fork. Sorry about that.

This commit addresses the comments made in the review of the previous pull request.

Thanks again.

[k8s-ci-robot]

Hi @hangongithub. Thanks for your PR.

I'm waiting for a google or kubernetes member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[dashpole]

/ok-to-test

[hangongithub]

Can I get a quick review on this? Thanks!

[dashpole]

lgtm