Bluetooth: Send proper track number

As per specification
RegisterNotification - If no track is currently selected
then return 0xFFFFFFFFFFFFFFFF in the interim response.
Changes are made to ensure return above value if play state
is not playing.

Change-Id: Ib27eeeb65fe6659178658e58eb8f875168b236df
CRs-Fixed: 519337
(cherry picked from commit 5676595caa52f85c369afb9b29119805c63577a9)
(cherry picked from commit b47f4c8a3e7b935cfeda2ebe506e54f903a5ed5e)
(cherry picked from commit f67097224dd89786b58d3d5d62775c15b7d03cd4)