Created GetIptablesMode to log legacy or nftables backend

[cdirubbio]

What type of PR is this? improvement

Which issue does this PR fix?:

What does this PR do / Why do we need it?: /usr/sbin/iptables-wrapper picks the iptables backend used based on a few conditions. With this change, a method is introduced to get the iptables mode (either nf_tables or legacy) in-use.

The package go-iptables that the vpc cni uses to interact with iptables is no longer being maintained, so this is the current solution. Following this change, we get the following log line during startup, prior to creation and insertion of iptables rules.

{"level":"info","ts":"2026-01-08T00:37:15.024Z","caller":"networkutils/network.go:377","msg":"Using iptables mode (nf_tables)"}

Testing done on this change:

Will this PR introduce any new dependencies?:

Will this break upgrades or downgrades? Has updating a running cluster been tested?:

Does this change require updates to the CNI daemonset config files to work?:

Does this PR introduce any user-facing change?:

Add GetIptablesMode() function to log iptables backend in-use

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.