Ignore the Class Of Device if the value is invalid

If a Bluetooth Device is dual-mode and is discoverable as both
a Classic and a LE device, ignore unknown "zero" values
triggered by the LE advertisements. Otherwise, those could overwrite
a valid (previously discovered) Class Of Device.

Bug: 37615863
Test: Manual with LG HBS1100 headset
Change-Id: I5a0f6ef56248b41d973b850a5542475e45e0312d