Add support for NFT with Calico and Canal

[hakman]

Newer distros like Debian 10 and RHEL/CentOS 8 are using iptables 1.8 which defaults to NFT backend. Kubernetes 1.17 adds support and auto-detection for it. From the release notes:

The official kube-proxy image (used by kubeadm, among other things) is now compatible with systems running iptables 1.8 in “nft” mode, and will autodetect which mode it should use. (#82966)

Calico doesn't yet have auto-detection for the iptables backend, but has a flag named IptablesBackend (env var FELIX_IPTABLESBACKEND) that can switch from Legacy to NFT:
https://docs.projectcalico.org/v3.9/reference/felix/configuration#iptables-dataplane-configuration

Without this flag Debian 10 networking is broken in Kubernetes 1.17.0. Kubernetes auto-detects NFT and uses it, but Calico still uses legacy, which is an unsupported behaviour.

[k8s-ci-robot]

Hi @hakman. Thanks for your PR.

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[hakman]

/cc @KashifSaadat
/cc @zetaab

[KashifSaadat]

Thanks @hakman !

/ok-to-test
/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hakman, KashifSaadat

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[KashifSaadat]

If you can run make crds it should sort out the test failures.

[KashifSaadat]

Perfect, thanks!

/lgtm

[hakman]

Thanks @KashifSaadat. Will cherry-pick also to 1.17 later today.