OpenVPN: Update to version 2.4.5

OpenVPN: Update to version 2.4.5

This is primarily a maintenance release, with further improved OpenSSL 1.1 integration, several minor bug fixes and other minor improvements.
Further information can be found in here https://github.com/OpenVPN/openvpn/blob/release/2.4/Changes.rst#version-245 and
here https://community.openvpn.net/openvpn/wiki/ChangesInOpenvpn24 .

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