[PATCH v5 2/4] eal: allow applications to report their cpu usage

[Konstantin Ananyev]

> 
> Konstantin Ananyev, Jan 04, 2023 at 11:53:
> > Probably we can even print warning or so if some-one tries to overwrite
> > it once again.
> 
> I'm not sure that is necessary. If an application wants to reset the
> callback to NULL at any point in time, I don't see why DPDK should tell
> them it is a bad thing.

Problem is not in resetting cb function itself.
Usually with CB user needs some sort of data structure (to accumulate stats, track states, etc.).
If we allow to reset the CB, then it arises the question when/how should we allow
user to free associated data?
And, as I undersand, we don't have a clear way to do it.