further bpf_existence_test code simplifications/clarifications am: e9e7741872 am: a26668aa53

Original change: https://android-review.googlesource.com/c/platform/packages/modules/Connectivity/+/2156256

Change-Id: I0d04f2eaef84d5572c4459d6ed48c4d7bc0246b6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>