fix: link unknown should not be categorized as down

[starbops]

Problem:

Links that are not up will be considered as down.

Solution:

Links that are in the unknown state should be reflected genuinely in the LinkMonitor CR.

Related Issue:

harvester/harvester#9140

Test plan:

1. Create a ClusterNetwork
2. Create a VlanConfig for the ClusterNetwork
3. Check the LinkMonitor

[Copilot]

Pull request overview

This PR fixes an issue where network links with an unknown operational state were incorrectly being categorized as "down". The change introduces a new LinkUnknown state to properly represent links that are not explicitly up or down.

Changes:

• Added a new LinkUnknown constant with value "unknown" to the LinkState type
• Refactored the link state determination logic from if-else to a switch statement that properly handles all netlink operational states

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
pkg/apis/network.harvesterhci.io/v1beta1/linkmonitor.go	Adds new LinkUnknown constant to support unknown link states
pkg/controller/agent/linkmonitor/controller.go	Updates linkToLinkStatus function to use switch statement and map unknown OperState values to LinkUnknown instead of LinkDown

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[rrajendran17]

Thanks for the changes.Can you also generate a new linkmonitor crd with updated enum "unknown" in manifests/crds/network.harvesterhci.io_linkmonitors.yaml from the api and also update https://github.com/harvester/charts/blob/master/charts/harvester-network-controller/templates/crds/network.harvesterhci.io_linkmonitors.yaml