Add dual-stack support for NPL and NodePort

[Qwiko]

My attempt to resolve #1535. Would like some input from the maintainers if this approach is a good one. In PopulateServersForNPL there is some duplicate code now that could be tweaked further. Also: I have not looked over PopulateServers in this PR but would like some input if this also needs to be tweaked to fully support dual-stack support.

[vmwclabot]

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[Dhivyaaj]

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[akshayhavile]

Can one of the admins verify this patch?

[vmwclabot]

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[vmwclabot]

@Qwiko, VMware has rejected your signed contributor license agreement. The merge can not proceed until the agreement has been resigned. Click here to resign the agreement. Reject reason:

test reject

[vmwclabot]

@Qwiko, VMware has approved your signed contributor license agreement.