LeAudio: Check for start request mutext before getting value am: 4fa63586 am: 958c502f

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Bluetooth/+/3006539



Change-Id: Iccde07c1f70981811463a074f6caa7f3b91b9776
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>