OCPBUGS-82519: Fix chronyd NTP failover

[vitus133]

stop/start chronyd process instead of chronyc offline/online

The chronyc offline command was unreliable — chronyd could re-acquire NTP sources despite being told to go offline, causing clock frequency interference with phc2sys (clockcheck events). Replace with process stop/start, using the same pattern as phc2sys.

The disable path uses go p.cmdStop() (non-blocking) to avoid a deadlock: cmdStop blocks on exitCh, but the ntpfailover FSM callback runs inside the process scanner goroutine which must finish before cmdRun can send to exitCh.

[openshift-ci-robot]

@vitus133: This pull request references Jira Issue OCPBUGS-82519, which is invalid:

• release note text must be set and not match the template OR release note type must be set to "Release Note Not Required". For more information you can reference the OpenShift Bug Process.
• expected Jira Issue OCPBUGS-82519 to depend on a bug targeting a version in 4.21.0, 4.21.z and in one of the following states: VERIFIED, RELEASE PENDING, CLOSED (ERRATA), CLOSED (CURRENT RELEASE), CLOSED (DONE), CLOSED (DONE-ERRATA), but no dependents were found

Comment /jira refresh to re-evaluate validity if changes to the Jira bug are made, or edit the title of this pull request to link to a different bug.

The bug has been updated to refer to the pull request using the external bug tracker.

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In response to this:

stop/start chronyd process instead of chronyc offline/online

The chronyc offline command was unreliable — chronyd could re-acquire NTP sources despite being told to go offline, causing clock frequency interference with phc2sys (clockcheck events). Replace with process stop/start, using the same pattern as phc2sys.

The disable path uses go p.cmdStop() (non-blocking) to avoid a deadlock: cmdStop blocks on exitCh, but the ntpfailover FSM callback runs inside the process scanner goroutine which must finish before cmdRun can send to exitCh.

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[openshift-ci]

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