Set TLS 1.2 as minimum by default

Set TLS 1.2 as minimum by default

Do not accept handshakes with peers trying to negotiate TLS lower than 1.2.

TLS 1.1 and 1.0 are not recommended and therefore we will, by default,
allow TLS 1.2 as minimum version.

The minimum allowed version can still be controlled via
'--tls-version-min'.

At the same time automatically set '--tls-version-min' to 1.0 if the
user requires compatibility with versions onlder than 2.3.7, as that was
the only version supported back then.

Signed-off-by: Arne Schwabe <arne@rfc2549.org>
Signed-off-by: Antonio Quartulli <a@unstable.cc>
Acked-by: Gert Doering <gert@greenie.muc.de>
Message-Id: <20210913192929.26391-1-a@unstable.cc>
URL: https://www.mail-archive.com/openvpn-devel@lists.sourceforge.net/msg22838.html
Signed-off-by: Gert Doering <gert@greenie.muc.de>