Merge "clat: make sure the tun device doesn't yet exist" am: 5d8992e2b1

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2535059

Change-Id: I8df66eb17b97acbccf4125cc7b395c10b7590fbc
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>