security/openvpn: fix regressions and some documentation bits

Add two patches cherry-picked from upstream Git repository:

OpenVPN 2.6.7 regressed and experienced crashes in some situations,
https://github.com/OpenVPN/openvpn/issues/449
Reported by: Vladimir Druzenko (vvd@)
Reported by: Patrick Cable (upstream)
Obtained from: https://github.com/openvpn/openvpn/commit/b90ec6dabfb151dd93ef00081bbc3f55e7d3450f

Also, some typos in the documentation are fixed,
Obtained from: https://github.com/OpenVPN/openvpn/commit/457f468a76f324a14b1236988cc5f5a95f14abf5

Bump PORTREVISION.
PR: 275055
MFH: 2023Q4