In 9.10 I was able to add tap interfaces (previously created in tunables) to the UI. And give them address and all from the UI.
At some point this feature disappeared, I guess it was in 11.something. And since then, only physical interfaces can be added to this section.
I see this as a regression, since this feature allowed to create host-only networks, and bind services only to virtual machines, granting a wonderful test environment. Also