AVDTP: Reject the start request while SCO is up

Some Bluetooth headsets can't handle AVDTP media and SCO at the same
time, and we have checked the call state to prevent such case. However,
if there was a voice recognition running over the Bluetooth SCO, it was
call idle. Now we listen to the SCO status, so AVDTP media won't be
started at the same time.

Bug: 139520575
Test: manually
Change-Id: I70377cf531bf6c4b56dc51a84d2c8ead6a7fdc39