leaudio: Improve disabling stream

With this patch, group state machine will send Disable command
simultaneously to all active devices.

Bug: 265501806
Test: atest bluetooth_le_audio_test
Test: atest BluetoothInstrumentationTests
Tag: #feature
Change-Id: Iaed6f7e6f93b93e459794f5e168ec3c907d5bc0f