further bpf_existence_test code simplifications/clarifications am: e9e7741872 am: a757505f31 am: 6485b462f8

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

Change-Id: I2c1694984025b070d3abbc37b28358a97f7940c6
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>