Register for Service Changed notifications for untrusted devices

As required by Bluetooth Spec 4.2 [Vol 3, Part G] 2.5.2:
Clients without a trusted relationship shall receive an indication
when the service change occurs only during the current connection.

This means that even we're not paired, we should still register
and receive Service Changed.

Change-Id: Ifd6b69f4cdef6d7114a596221d2dd290a3b7044f