v3 idea. Make "ad" part of tchannel

[Raynos]

There are two relevant issues/PRs

• Hyperbahn should advertise to you as a router ( hyperbahn incoming socket advertisement #487 )
• A proposal for "ad" ( v3: Proposal for advertisement. #444 )

There has been discussion of adding "ad" as a first class thing to tchannel.

This will be useful for more use-cases as once the init and ad requests have finished you will be able to know what service names a particular connection implements.