Add OpenVPN 2.4 ECDH options
OpenVPN 2.4 added two ECDH-related options:
1. Settings "dh" to "none" tells OpenVPN to use only ECDH and not DH
2. Added the "ecdh-curve" option to select a specific ECDH curve
2a. To get a list of possible curves, use openvpn --show-curves
To me, I've got some code I've been experimenting with.