bpf_base_test: fix cgroup2 hardcoded path the path for cgroup2 was moved to its canonical position by https://r.android.com/c/1324649/5. Move the hardcoded equivalent to the same path. Test: presumit tests pass Bug: 171770637 Bug: 154548692 Change-Id: I50f7a2385b7de88818ac60b0bcd6b92d711e6e16 (cherry picked from commit 467687c40fbc9e5dfd2eeed0b9221dd2d9bfc060)