Add support for routed IPv6 blocks

[lucyrose39]

Is your feature request related to a problem? Please describe.
Add the ability to use a routed IPv6 block instead of forcing NAT. IE; using public IPspace on the tunnel segment instead of private IPv6 space.

Describe the solution you'd like
Implement the ability to disable NAT on IPv6, and use a routed IPv6 block instead.

Describe alternatives you've considered
There is no alternative. This is a feature that is not completely replaceable with NAT or other networking bandaids