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

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

Change-Id: I5d8cfbfa7eae995335e1715f3df08210f0a36fe4
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>