HFP: Set active device when SLC is done, active device is null

When SLC is connected with a device and active device is null,
set the device as active device from HeadsetService. This will
help in call audio routing to the device without delay if an
active call is present during SLC.

CRs-Fixed: 2334228
Change-Id: I9a52c56350cc0aa860bb0093c3cac3b98c1f8b78
1 file changed