add flowtable object

[aojea]

Add flowtable object based on https://www.netfilter.org/projects/nftables/manpage.html

[aojea]

/hold

pending testing with kubernetes

[aojea]

/hold cancel

addressed comments

[aojea]

@danwinship incorporated the patch you shared via slack that fixes the problems with the kube-proxy unit tests kubernetes/kubernetes#128392 (it fails only the test that expect certain number of transactions now, but since we are going to make the feature opt-in I will not modify the tests now, just we know this has been fixed)

The other problem was in the regex to get the list of devices between the curly brackets, now I just copied from your logic for the comments, it gets everything inside the curly brackets and trims the spaces

This now is ready to go

[danwinship]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: aojea, danwinship

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