Clarify tunnel bring down reason for tunnel closure.

Add bring down reason for each utilization of closeTunnel() Api.

Bug: 309866889
Test: atest IwlanTests
(cherry picked from https://googleplex-android-review.googlesource.com/q/commit:2851ad69e00923cb42f413a1186a804b985e021b)
Merged-In: I8de66471b7e3dc7f2e92c7e3ab1cbe749162272b
Change-Id: I8de66471b7e3dc7f2e92c7e3ab1cbe749162272b
4 files changed