Declare new interface for headset client bluetooth profile to query.

This is needed in order to allow implementations of the HFP HF side to
define when audio can be routed to the device. This allows for calls dialed
from an AG to be kept on the AG if desired.

Bug: 25332357
Change-Id: I35a554cfc53f88c7dd3059bf52df5c69df9c7415