Clarify Project Policy on Default Writes to NVRAM

[Goetz Goerisch]

Thank you Ansuel,

> We need to save it only on reboot so we don't need to write stuff
> periodically every day.

For clean reboots, fully agree.

> Aside from panic conditions that we can't handle, we can attach any
> kind of logic to be
> done when reboot is called.

RFC9096 especially addresses the crash-and-reboot case:
...
> 1 Introduction
> In scenarios where network configuration information becomes invalid
> without any explicit signaling of that condition (such as when a
> Customer Edge (CE) router crashes and reboots without knowledge of
> the previously employed configuration information), hosts on the
> local network will continue using stale information for an
> unacceptably long period of time, thus resulting in connectivity
> problems.
...

Therefore in current state this would mean one write / 24h if RFC9096
should be fully supported.