bhyve tapN additions

[Peter Grehan]

Hi Allan,

> The tap device can also be created automatically by bhyve, make sure you
> specify a different tap device for each instance of bhyve.

  That may require some devd scripting to get it to be added to a bridge 
group.

  We're looking at having the bridge interface have a cloneable 
tap-style interface so this step can be avoided i.e. point bhyve at a 
/dev/bridgeN device, and it will automatically become a part of that bridge.

later,

Peter.