selftests/bpf: Bail out quickly from failing consumer test

Let's bail out from consumer test after we hit first fail,
so we don't pollute the log with many instances with possibly
the same error.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>