refactor: use netip.AddrPort

[alexandear]

This PR changes the fields of iptables.Entry from IP net.IP and Port int to AddrPort netip.AddrPort. This results in slightly simpler code, and iptables.Entry becomes comparable.

net.IP is not comparable because slices in Go are not comparable.

[jandubois]

I can't spot where the error comes from, but port-forwarding tests are failing.

With Fedora:

❌ Forwarding TCP from [::]:4024 to 10.1.0.209:4024
     Guest received: ''

It is not always the same one that fails though:

 ❌ Forwarding TCP from 127.0.0.2:4031 to 10.1.0.209:4031
     Guest received: ''

With Alpine:

 ❌ Forwarding TCP from 127.0.0.2:4021 to 10.1.0.142:4021
     Guest received: ''

I will run the tests one more time, but I think the same set of 3 tests failed both times.

[alexandear]

I can't spot where the error comes from, but port-forwarding tests are failing.

With Fedora:

❌ Forwarding TCP from [::]:4024 to 10.1.0.209:4024
     Guest received: ''

It is not always the same one that fails though:

 ❌ Forwarding TCP from 127.0.0.2:4031 to 10.1.0.209:4031
     Guest received: ''

With Alpine:

 ❌ Forwarding TCP from 127.0.0.2:4021 to 10.1.0.142:4021
     Guest received: ''

I will run the tests one more time, but I think the same set of 3 tests failed both times.

I'll take a look, thanks.