Add test for startPptp am: 522cea7d4e

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2133038

Change-Id: If5e0c46c9fc2da3866431383e0e3689f64acef61
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>