You can't (and shouldn't) disable IPv6 on the Xbox One.
The Xbox One mainly uses IPv6 to transfer it's multiplayer data, however, if IPv6 is not natively available, it'll use Teredo to tunnel IPv6 through IPv4.
So even if you only have IPv4 in your network, the console will still use IPv6.
Is there a specific reason why you wish to disable IPv6? Since IPv6 is actually better for multiplayer gaming, you would want to have it enabled.