Kubernetes: Update knftables to v0.0.20

Problem

kube-proxy's nftables support depended on an outdated knftables library version. The newer library version provides improved compatibility with current nftables versions.

Solution

Updated knftables dependency to v0.0.20. Verified compatibility with existing nftables rules and command parsing.

Result

Better nftables compatibility through updated dependency. Foundation for supporting newer nftables versions in kube-proxy.

Commit: kubernetes/kubernetes@62c3d8d