[Audiosharing] Disable main toggle till device gets active.

Broadcast <-> unicast costs some time, so we grey out the audio
sharing toggle until the device get active on unicast when users toggle
off the sharing.

Flag: com.android.settingslib.flags.enable_le_audio_sharing
Test: atest
Bug: 359755881
Change-Id: I868a470430f6fb54c142f17552d70fa5fa8a2476