cronet: add defaults to enable / disable Cronet in framework-tethering am: 3b9ba6acdf am: 29af3b6f8d

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2374722

Change-Id: I02340bcb6020241c9d82b03723c52f4d5b475e14
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>