pfPorts: Minor OpenVPN port sync with FreeBSD

Target is to identify and remove local modifications from our port
and sync against the regular OpenVPN port when it was at 2.2.0.
(FreeBSD ports r273590)

Our port was not based on openvpn but openvpn-devel port which are both
somewhat similar but have quite some differences even back then.

This commit should only sync minor things, in hope we don't miss relevant
local modofications when jumping on 2.3.0 which will bring fully integrated
IPv6 support.
Merge pull request #73 from matsimon/openvpn-2.3-migration

pfPorts: Minor OpenVPN port sync with FreeBSD