HFP connect Audio

Connect audio when a phonecall is started rather than relying on the
dialer to do it.  Due to complexities in SCO management and audio
routing only a single call is available and so upon answering a call
from a second phone the first call is terminated rather than held.

Bug: 62086689
Test: pair and connect 2 phones via HFP then make alternating incoming
and outgoing phone calls while ensuring that only 1 call remains active
and that call's audio is routed.
Change-Id: Iabb9cd6d483135feb93592cc8f8a33e042f2c41f