Align the logic with a2dp & le audio offload property concept

The property to control a2dp offload is
persist.bluetooth.a2dp_offload.disabled

Change the le audio property from enabled to disabled, it would make
some logic simpler as audio policy config selection.

Bug: 197296692
Test: make build
Change-Id: I128009b9cc91d413ebf50cd25675c7d0d2cbe7d2