Support more than one IP per interface and IPv6 for results returned by CNI

[th0m]

Our use case is to:

1. call SetupNetworkHandler ourselves to get the network configuration generated using a CNI plugin
2. remove firecracker.SetupNetworkHandlerName and firecracker.SetupKernelArgsHandlerName from the list of default FcInit handlers
3. use our own VM network interface configuration method instead of the default boot param based one
4. call machine.Start

With that in mind we want to be able to have more than one IP on interfaces and to support IPv6, which is what this change intends on achieving while keeping backwards compatibility.

[th0m]

@vvejell1 can you please help review this PR when you have a moment? Thank you.

[ginglis13]

Hi @th0m , looks like buildkite tests (example) have not run:

Missing DCO on d88daf38557b97d2922471b123748fd6aa2480cc

could you please sign your commit ? if you've already got your name and email configured in git, you can git commit --amend -s, then force push to this branch to update the PR

[th0m]

@ginglis13 I am getting build errors that seem unrelated to my change https://buildkite.com/firecracker-microvm/firecracker-go-sdk/builds/3007#01869a5d-b0c1-4d19-ad6f-156ddcc120f3/17-1015

[th0m]

@ginglis13 can you please have a look? Thanks

[ginglis13]

@th0m we've got an infrastructure bug we're addressing. As soon as it's resolved we can re-run and continue the review

[fangn2]

@th0m I have a fix on CI failure merged into main. You can rebase, push and trigger the build again.

[th0m]

Thanks, build failures are on me now, I will fix them.

[th0m]

Ready for review @fangn2 thank you.

[th0m]

@ginglis13 I believe this is ready to go.