further bpf_existence_test code simplifications/clarifications am: e9e7741872 am: a757505f31

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

Change-Id: Ie73d900822ff24482f58f36ff99ae85400bb35b5
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>