Handle null identity address in BluetoothOppManager

Add helper method to call into for profiles that connect over BR/EDR
transport, to accommodate the behavior correction where identity address
can be null. The helper method takes in a BluetoothDevice object and
returns the correct device address in String.

Bug: 317120534
Bug: 295907764
Test: m com.android.btservices
Change-Id: I3a4eaf882efda964f42479bf24b6435ea60448c6