Only calls to AudioManager.setBluetoothAudioDeviceCategory() can reset audio type to unknown

When connecting a new BT device and the BTHelper cannot find any
metadata for that device we do not want to reset the category to unknown
since the user could have set it before to a different value

Test: manual w/o automaticBtDeviceType
Bug: 328329062
Change-Id: Id9ec300a77efcc85cbc84fab66fb886d215fdabe