Implement methods to generate and manage OpenVPN Epoch keys

Implement methods to generate and manage OpenVPN Epoch keys

This implements functions that allow these keys to be generated and
managed. It does not yet implement using them for the data channel.

Change-Id: Id7d6a576ca8c9560cb2dfae82fc62175820e9b80
Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Acked-by: MaxF <max@max-fillinger.net>
Message-Id: <20250109180537.27686-1-gert@greenie.muc.de>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg30390.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>