Delay the second message for 30ms more than the last message for a2dp

In function setBluetoothA2dpDeviceConnectionState, current code calculate
the delay of the second state update message to be exactly the same as the
last delayed messages. This causes a problem that the sequence of the
messages may be altered.
Bug: 19036411

Change-Id: I35762873fd3341ec098dd229ac96bd42d6f34195