Make L4 NetLB Controller Healthcheck return error

[cezarygerard]

This is required to correctly track availability SLO when L4 NetLB Controller get's stuck

[k8s-ci-robot]

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[cezarygerard]

/assign @freehan @swetharepakula @kl52752

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/assign @freehan @swetharepakula @kl52752

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[swetharepakula]

/ok-to-test

[swetharepakula]

/lgtm
I will let @freehan review once and give final approval.

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: cezarygerard, swetharepakula

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[bowei]

Error not Errorf

[bowei]

error, not Errorf

[bowei]

Are we sure we want to immediately turn this healthcheck on vs having a flag and seeing how the metric behaves? If this is too sensitive when it rolls out to production, the only thing we can do at that point is to rollback.