iptables: Enable nftables

[Sumynwa]

Merge Checklist

All boxes should be checked before merging the PR (just tick any boxes which don't apply to this PR)

• The toolchain has been rebuilt successfully (or no changes were made to it)
• The toolchain/worker package manifests are up-to-date
• Any updated packages successfully build (or no packages were changed)
• Packages depending on static components modified in this PR (Golang, *-static subpackages, etc.) have had their Release tag incremented.
• Package tests (%check section) have been verified with RUN_CHECK=y for existing SPEC files, or added to new SPEC files
• All package sources are available
• cgmanifest files are up-to-date and sorted (./cgmanifest.json, ./toolkit/scripts/toolchain/cgmanifest.json, .github/workflows/cgmanifest.json)
• LICENSE-MAP files are up-to-date (./LICENSES-AND-NOTICES/SPECS/data/licenses.json, ./LICENSES-AND-NOTICES/SPECS/LICENSES-MAP.md, ./LICENSES-AND-NOTICES/SPECS/LICENSE-EXCEPTIONS.PHOTON)
• All source files have up-to-date hashes in the *.signatures.json files
• sudo make go-tidy-all and sudo make go-test-coverage pass
• Documentation has been updated to match any changes to the build system
• Ready to merge

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Summary

Enable building iptables with nftables to provide both iptables-legacy & iptables-nft with default being set to legacy.
This PR fixes https://microsoft.visualstudio.com/OS/_workitems/edit/53647336.

Change Log

• Enable build with nftables

Does this affect the toolchain?

NO

Associated issues

• https://microsoft.visualstudio.com/OS/_workitems/edit/54527124

Links to CVEs

Test Methodology

• Pipeline build id: Buddy Build

[mfrw]

Is this a breaking change ?

[Sumynwa]

The path xtables-multi does not exist and this becomes stale link. The correct path is added later in the commit (iptables.spec: L67)