Serialize the RC Cleanup events in BT-App context

-Race condition during RC cleanup and MediaController playback event
end up invoking NULL BD Address as an argument while sending play
status to remote. Byte conversion of that NULL address resulting in
SegFault. Hence send an RC cleanup message to AVRC handler to handle
the cleanup events sequentially.

-Put a NULL address check before responding the CHANGED response to
remote.

CRs-Fixed: 1086579
Change-Id: I766538debaec330c5694844c4b7145bc9402dc6e