Use OpenVPN Manager client management port if specified for the server concerned

If the OpenVPN server has the client management port field specified, then use that port number when generating the OpenVPN Manager client config file, otherwise use the default of "166".
See: forum.pfsense.org/index.php/topic,63668.0.html
Discussion: https://github.com/jochenwierum/openvpn-manager/issues/17
Related pull request on pfsense repo: https://github.com/pfsense/pfsense/pull/783