Kernel: T6230: add ipt_NETFLOW out-of-tree module

[c-po]

Change summary

Add build script for ipt_NETFLOW kernel module

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Code style update (formatting, renaming)
• Refactoring (no functional changes)
• Migration from an old Vyatta component to vyos-1x, please link to related PR inside obsoleted component
• Other (please describe):

Related Task(s)

• https://vyos.dev/T6230

Related PR(s)

Checklist:

• I have read the CONTRIBUTING document
• I have linked this PR to one or more Phabricator Task(s)
• My commit headlines contain a valid Task id
• My change requires a change to the documentation
• I have updated the documentation accordingly

[github-actions]

👍
No issues in PR Title / Commit Title

[sempervictus]

probably better to keep it at the rev it was using when the current minor version of the kernel was tagged (6.6) or thereabouts - it can drift on occasion requiring some backporting or recision. Generally though "works as advertised" and is extremely handy when hsflowd can't keep up.

I tried to find the userspace build script which put the pacakge i use in our repo but havent come across it so far. Will pull the kmod out of the big kernel patch for vyos as well next time i build to use/test this PR.