bpf is required so /sys/fs/bpf/map_netd_app_uid_stats_map always exists

(we cannot just remove the argument, since the test code path still
 goes via the legacy xt_qtaguid code paths with sample data)

Test: TreeHugger
Signed-off-by: Maciej Żenczykowski <maze@google.com>
Change-Id: I044d0363aaab0dbbb90c40ca466cc48f169d649a