Add Ubuntu support for 22.04 with nftables

[cobbzilla]

Is your feature request related to a problem? Please describe.
When installing on Ubuntu, Algo does not have any special support for the most recent version. In particular, iptables has been deprecated in favor of nftables.

Describe the solution you'd like
An installation onto Ubuntu 22.04 that uses nftables instead of iptables.

Describe alternatives you've considered
I've looked at adding this support myself but decided it was more than I could handle.

Additional context
No additional context.

[dguido]

Thanks for bringing this up! You're absolutely right that Ubuntu has moved to nftables as the default backend. However, the current situation is more nuanced than it first appears.

Current Status

Ubuntu 22.04+ does use nftables as the kernel backend, but maintains full backward compatibility through iptables-nft. When Algo runs iptables commands, they're automatically translated to nftables rules under the hood. So we're technically already using nftables - just through the iptables compatibility interface.

Why We Haven't Migrated to Native nftables

1. Current approach works perfectly - no functional issues on Ubuntu 22.04/24.04
2. Cross-platform compatibility - we support multiple OS targets that may not have native nftables
3. Complexity vs. benefit - rewriting firewall rules would be a significant effort for minimal practical gain in VPN server scenarios

Future Considerations

That said, there are some compelling reasons to consider native nftables in the future:

• Cleaner rule organization - nftables has better syntax for complex rule sets
• Better IPv4/IPv6 integration - single ruleset instead of separate v4/v6 files
• Performance improvements - though minimal for typical VPN workloads
• Future-proofing - aligning with Ubuntu's preferred direction

Proposal

I'm inclined to keep this open for a future 3.0 milestone, but it's not a high priority since:

1. Current implementation works fine
2. We're focusing on Ubuntu 24.04 migration (Update Algo VPN to Support Ubuntu 24.04 LTS #14812) first
3. We may simplify our platform support matrix (potentially dropping some BSD targets)

Once we streamline our supported platforms, implementing native nftables becomes more feasible as we'd have fewer compatibility constraints to juggle.