Clarify tunnel bring down reason for tunnel closure. am: 2bb7b2a4be

Original change: https://android-review.googlesource.com/c/platform/packages/services/Iwlan/+/2968802

Change-Id: Iec8f369a86bdde159166b3260e633719ee13b1a6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>