OpenVPN: Add tls-version-min for TLSv1.2

OpenVPN: Add tls-version-min for TLSv1.2

ovpnmain.cgi delivers now 'tls-version-min 1.2' for Roadwarrior and N2N.
Since the server needs it only on server side, this patch do not includes it for Roadwarrior clients.
N2N do not uses push options therefor this directive will be included on both sides.

To integrate the new directive into actual working OpenVPN server environment, the following commands
should be executed via update.sh.

Code block start:

if test -f "/var/ipfire/ovpn/server.conf"; then
	# Add tls-version-minimum to OpenVPN server if not already there
	if ! grep -q '^tls-version-min' /var/ipfire/ovpn/server.conf > /dev/null 2>&1; then
		# Stop server before append the line
		/usr/local/bin/openvpnctrl -k
		# Append new directive
		echo >> "tls-version-min 1.2" /var/ipfire/ovpn/server.conf
		# Make sure server.conf have the correct permissions to prevent such
		# --> https://community.ipfire.org/t/unable-to-start-the-openvpn-server/2465/54?u=ummeegge
		# case
		chown nobody:nobody /var/ipfire/ovpn/server.conf
		# Start server again
		/usr/local/bin/openvpnctrl -s
	fi
fi

Code block end

Signed-off-by: Erik Kapfer <ummeegge@ipfire.org>
Signed-off-by: Michael Tremer <michael.tremer@ipfire.org>