Comparing address strings instead of device references

In some cases, there can be multiple BluetoothDevice objects of the same
address. This happens specially during scanning. So we should always
compare addresses instead of the BluetoothDevice objects.

Bug: 244499372
Test: atest BluetoothInstrumentationTests
Tag: #stability
Change-Id: I259ad8d39817b2994e9d437337e4d4b03e9801c6