Change the toggle from "Enable LE audio" to "Disable LE audio"

- Adopt system property persist.bluetooth.leaudio_switcher.disabled
  to check the developer option toggle status

Bug: 275388899
Test: atest BluetoothInstrumentationTests
Test: Manual, switch LE audio toggle in developer option, and check LE audio functionality status
Change-Id: Idd14bcb89b4370853d674acab0855848ffd762f8