Fix lint failures spotted after upgrading to Go 1.23

[jingyuanliang]

pkg/metrics/collector/pod_ip_metrics.go:322:2: builtinShadow: shadowing of predeclared identifier: max (gocritic)
	max := uint64(1) << uint(bits-ones)
	^
pkg/metrics/collector/pod_ip_metrics.go:[235](https://github.com/GoogleCloudPlatform/netd/actions/runs/10693607402/job/29644029691?pr=350#step:3:236):3: ifElseChain: rewrite if-else to switch statement (gocritic)
		if !ok {
		^
pkg/metrics/collector/pod_ip_metrics_test.go:214:2: commentFormatting: put a space between `//` and comment text (gocritic)
	//Add a new file to the directory. Verify metrics
	^
pkg/metrics/collector/pod_ip_metrics_test.go:233:2: commentFormatting: put a space between `//` and comment text (gocritic)
	//Remove a file from the directory. Verify metrics
	^
pkg/metrics/collector/pod_ip_metrics_test.go:274:3: ifElseChain: rewrite if-else to switch statement (gocritic)
		if !ok {
		^
pkg/config/config_test.go:52:18: unused-parameter: parameter 'route' seems to be unused, consider removing or renaming it as _ (revive)
		RouteAdd: func(route *netlink.Route) error { return os.ErrExist },
		               ^
pkg/config/config_test.go:53:18: unused-parameter: parameter 'route' seems to be unused, consider removing or renaming it as _ (revive)
		RouteDel: func(route *netlink.Route) error { return syscall.ESRCH },
		               ^
pkg/config/config_test.go:84:18: unused-parameter: parameter 'family' seems to be unused, consider removing or renaming it as _ (revive)
		RuleList: func(family int) ([]netlink.Rule, error) { return ruleList, nil },
		               ^