Update istio iptables CLI to specify DNS redirection

[coodie]

In current state it is impossible to reasonably use dns redirection to agent when imported iptables package is used by other golang module. Environmental variable "ISTIO_META_DNS_CAPTURE" is added as global private module variable forcing potential users of the library to have to set up this variable in environment before their binary is up and running.

This change fixes that problem by simply adding "redirect-dns" option to iptables CLI, making it possible to use dns redirection directly from within go code that imports that package without having to set up environmental variable.

[ ] Configuration Infrastructure
[ ] Docs
[ ] Installation
[x] Networking
[ ] Performance and Scalability
[ ] Policies and Telemetry
[ ] Security
[ ] Test and Release
[ ] User Experience
[ ] Developer Infrastructure

[ ] Does not have any changes that may affect Istio users.

[istio-policy-bot]

😊 Welcome @coodie! This is either your first contribution to the Istio istio repo, or it's been
awhile since you've been here.

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[istio-testing]

Hi @coodie. Thanks for your PR.

I'm waiting for a istio 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.

[howardjohn]

/ok-to-test

[coodie]

/retest

[coodie]

/retest