Serialize access to TunnelConfig on session closed am: dec64d5a04 am: 07491269cd

Original change: https://googleplex-android-review.googlesource.com/c/platform/packages/services/Iwlan/+/18003976

Change-Id: Iffcf8c0eed61cebf4edac1e379e169afbf456498
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>