pkg/proxy: Simplify LocalTrafficDetector

[danwinship]

What type of PR is this?

/kind cleanup

What this PR does / why we need it:

Now that we don't have to always append all of the iptables args into a single array, there's no reason to have LocalTrafficDetector take in a set of args to prepend to its own output, and also not much point in having it write out the "-j CHAIN" by itself either.

Which issue(s) this PR fixes:

none

Special notes for your reviewer:

spinoff from #106497

Does this PR introduce a user-facing change?

NONE

/sig network
/assign @thockin
/triage accepted

[thockin]

Thanks!

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: danwinship, thockin

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[k8s-triage-robot]

The Kubernetes project has merge-blocking tests that are currently too flaky to consistently pass.

This bot retests PRs for certain kubernetes repos according to the following rules:

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• The PR does not have the needs-ok-to-test label
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