Detect and alter user if we can't detect public IP for server
The OpenVPN server makes sense pretty much only with public IP. In most cases we should be able to verify IP address assigned to WAN (if it is not from blocks reserved for on-site networks) but that is not 100% (think about 1:1 NAT and other stupid stuff) thus we should only display warning.
I am not sure if we support client connecting over IPv6 but I think that:
- warning that OpenVPN server probably won't work should be if user misses IPv6 and has private IPv4.
- notice if he has IPv6 about limitations of running OpenVPN server on IPv6 only (such as no access from IPv4 network) If user has IPv6 and private IPv4