stack_manager: Hide implementation of legacy acl layer am: 96e60b39 am: c890cac6

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Bluetooth/+/3012394



Change-Id: I621b9c6938765f8019161625d50930ef2c398ad7
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>