From: Lars Ellenberg <lars.ellenberg@linbit.com>
Date: Tue, 3 May 2016 12:06:44 +0200

Whereas using some arbitrary value will be wrong,
and will needlessly break userland.

It cannot break userland.

A fundamental property of netlink is that all code must silently
ignore netlink attributes it does not understand.

This is why netlink is easily extensible.

If code isn't doing that, it is broken and must be fixed.