Bluetooth: DUN: Add DUN profile support in Settings APP

This patch registers service listener for DUN profile with the
BT adapter, and it will track the profile status with the service
listener state chnages. It also has support for DUN profile
connection status updation and DUN Disconnection from server.

Change-Id: I6bd0069b3619b3487433c2e05f1e27ce9375a7e7
CRs-Fixed: 557180