Active ceph-mgr crashes on receiving report from a non-active mgr

[Ponnuvel Palaniyappan]

[Impact]
An active ceph-mgr crashes and another ceph-mgr takes over and becomes
the active mgr. But this could again hit same issue and crash and the cycle can continue indefinitely (previously crashed ceph-mgr gets restarted by systemd).

This could affect the cluster stability/usability as ceph mgr handles a number of essential operations (modules that control/change Ceph cluster behaviour, metrics, etc).

[Test Plan]
Deploy and operate a Ceph cluster normally.
Increase the log level of mgr to 20.
Observe MMgrReport sent from non-active mgrs get ignored (no crash).

[Where problems could occur]
Possibly the fix may not actually fix and mgr continue to crash as before.
Might incorrectly ignore reports from active mgrs.

[Other Info]
Upstream main bug: https://tracker.ceph.com/issues/48022
Octopus backport PR: https://github.com/ceph/ceph/pull/43861
Octopus backport bug: https://tracker.ceph.com/issues/53198

This has been already been fixed and available in Pacific.
So needed to backport only for Octopus.

[Ponnuvel Palaniyappan (pponnuvel)]

Attaching debdiff for Focal.

[Brian Murray (brian-murray)]

An upload of ceph to focal-proposed has been rejected from the upload queue for the following reason: "The patch d/p/bug1955345.patch doesn't actually appear in the debdiff or d/p/series file.".

[Ponnuvel Palaniyappan (pponnuvel)]

This has been superseded by https://bugs.launchpad.net/ubuntu/+source/ceph/+bug/1964802
which is a newer Octopus release (15.2.16) and contains the commits for fixing this as well.