Add support for CTNETLINK messages

[terassyi]

Hi!
I want to add support for CTNETLINK messages for handling Linux netfilter conntrack subsystem.

For example, golang implementation is following.

• https://github.com/vishvananda/netlink/blob/main/conntrack_linux.go

I'm already working for the PR.
If I submit the PR, could you review it?
Its PR will be quite big, so I also can split multiple PRs.

Thanks!

[terassyi]

Hi, @cathay4t
I believe you are one of the main maintainers.
I’ll create the PR as described above.
Could you please review it?

[cathay4t]

Hi,

I am not expert on this crate, @dzamlo might be better.

I am open to learn new stuff, if @dzamlo failed to find time for your patch.

[dzamlo]

Hi,

I didn't touch this crate or netfilter for some time, so I'm not an expert anymore.

[reyzell]

Hi there, I opened pull request #10 to expose conntrack new & destroy events, before I realized #9 covered similar functionality. It looks like #9 supports all conntrack messages. @terassyi is that right? Should we discard #10 or does it offer anything new?

[terassyi]

Hi, @reyzell!

This pull request supports almost all conntrack messages except expect table.