Whitelist local IPv6 CIDRs when airgapping nodes

[twz123]

Description

This does the same to IPv6 that's done for IPv4. Allows the airgap test to function if the SSH connection runs via IPv6. Also: check if ip6table_filter is already loaded before trying to modprobe it. This allows the integration test to work without sudo/doas when the module is already loaded.

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

How Has This Been Tested?

• Manual test
• Auto test added

Checklist:

• My code follows the style guidelines of this project
• My commit messages are signed-off
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules
• I have checked my code and corrected any misspellings

[twz123]

Apparently something changed on the GitHubGitHub Runner Image between 20240603.1.0 and 20240609.1.0 which makes the airgap tests fail? This seems to fix it... 🤔

[k0s-bot]

Successfully created backport PR for release-1.30:

• [Backport release-1.30] Whitelist local IPv6 CIDRs when airgapping nodes #4610