Add special support for IPAddress.None for servers

Fixes #420
This line should be

``` csharp
/// <param name="accessIPv6">The new IP v6 address for the server, or <see cref="IPAddress.None"/> to remove the configured IP v6 address for the server. If the value is <see langword="null"/>, the server's IP v6 address is not updated.</param>
```