BT: Synchronize Bond SM message processing and cleanup

Problem: Bond State Machine cleanup while processing of
a message cause a application exit because of
dereference of cleaned up objects.

Fix: Serialize BondStateMachine cleanup and processing
of messages.

CRs-Fixed: 2287412
Change-Id: I0f1be81fd9d596968883e9a6759a619dced50624
1 file changed