Add --tls-version-max

Because using TLS 1.2 breaks certain setups, a user might want to enforce
a maximum TLS version to use. This patch adds that option.

This patch removes a number of #ifdefs from ssl_polarssl.c, because the
polarssl versions we currently support (polar 1.2 for openvpn 2.3, and
polar 1.3 for openvpn-master) have all versions unconditionally enabled.

Signed-off-by: Steffan Karger <steffan.karger@fox-it.com>
Acked-by: Arne Schwabe <arne@rfc2549.org>
Message-Id: <544EC052.3080809@fox-it.com>
URL: http://article.gmane.org/gmane.network.openvpn.devel/9210
Signed-off-by: Gert Doering <gert@greenie.muc.de>