Add test for startPptp am: 522cea7d4e am: 7db77178ec am: 7706101aeb

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

Change-Id: I66813bbc638a2f8ff36f4a2bd883395af35c7b06
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>