BT: Use static lock to avoid race while cleanup
Problem:
The functions protected by mutex lock are called after cleanup
during shutdown. During this race condition, the structure set does not
exist and cause crash.
Steps:
Bluetooth on/off automation
Failure:
Bluetooth process crashes
RootCause:
Mutex is accessed after it is destroyed because of other thread calling
the function.
Fix:
Changed mutex lock to static type so that it exist and protect
the set structure even after cleanup.
Test: manual
Bug:
66921327
Change-Id: I8d1f5d5d607100ab73aec722a27688dae45cc323