debug: option to print using mnl format

[aojea]

nftables uses the libmnl library that has a particular debugging format. This format is also used for nftables --debug=all. google/nftables golang library to interact with nftables uses this library to interface with netlink directly.
Since the netlink libraries and implementations are not well documented, is common to have to dump the netlink bits to compare.

This commit implements an option to choose the same format used in nftables by adding a new option to the NLDEBUG environmental variable and using the format=mnt key value.

Output of nft --debug=all

Output of a nftables dump using google/nftables and setting the environment variable
https://gist.github.com/aojea/8a811e11a060fa638aa2dd8165960d5a

NLDEBUG=format=mnl go run main.go cni-kindnet prerouting

cc: @stapelberg

[stapelberg]

Thanks for your PR!

[mdlayher]

This is awesome, I would be fine making this the default debugging format given that the existing one is probably not very useful for most circumstances.

I do think that the printer is complex enough to probably at least merit a unit test that dumps a fixed output and verifies that it does not drift.

[aojea]

This is awesome, I would be fine making this the default debugging format given that the existing one is probably not very useful for most circumstances.

I do think that the printer is complex enough to probably at least merit a unit test that dumps a fixed output and verifies that it does not drift.

@mdlayher added a commit to bump github actions and golang versions and defaulted the logger to mnl

[aojea]

@mdlayher my apologies, somehow I didn't realize the PR was not updated until today, it should be ready for review now