AudioService: fix a2dp force use delay

Fixed setBluetoothA2dpOnInt() so that AudioSystem.setForceUse()
is called synchronously and not via a message.

This is because the order in which setForceUse() and setDeviceConnectionState()
are executed is important to avoid audio glitches when called from
onSetWiredDeviceConnectionState().

Bug 6720482.

Change-Id: I09c975d1108fd38f31b047c082acdf944ab790a7