OBEX: Implementation of MAP and PBAP client role on Bluedroid

Implementation changes to support MAP client and PBAP client
role on Bluedroid stack.

Change-Id: Ic75e0bea10b8420aef928d868cc25acd769d5620
CRs-fixed: 530274
Bluetooth: Add error handling for callbacks in bluetooth manager

This adds null pointer check for callback before using it.

Change-Id: Ic04e5e9c766b79c9bf483f19b3b3bd7e240b4693
CRs-Fixed: 542151