compat-mode: allow user to specify version to be compatible with

compat-mode: allow user to specify version to be compatible with

This changes introduces the basic infrastructure required
to allow the user to specify a specific OpenVPN version to be
compatible with.

The next commits will modify defaults to more modern and safer
values, while allowing backwards-compatible behaviour on demand.

The backwards-compatible behaviour is intructed via the config
knob '--compat-mode' implemented in this patch.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by:
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210908072606.5863-1-a@unstable.cc>
URL: https://www.mail-archive.com/search?l=mid&q=20210908072606.5863-1-a@unstable.cc
Signed-off-by: Gert Doering <gert@greenie.muc.de>