Expose ports for IPSec

Hey,

I've been trying to get your image running with IPSec, but it needs a couple of new ports opened up.
I took the required ports from https://www.softether.org/3-spec and others.

> L2TP/IPsec Sever Function Specifications on SoftEther VPN Server
...
Transport UDP Ports:
UDP 500 and 4500
...