selftests/bpf: test_progs use another shell exit on non-actions

This is a follow up adjustment to commit 6c92bd5c ("selftests/bpf:
Test_progs indicate to shell on non-actions"), that returns shell exit
indication EXIT_FAILURE (value 1) when user selects a non-existing test.

The problem with using EXIT_FAILURE is that a shell script cannot tell
the difference between a non-existing test and the test failing.

This patch uses value 2 as shell exit indication.
(Aside note unrecognized option parameters use value 64).

Fixes: 6c92bd5c ("selftests/bpf: Test_progs indicate to shell on non-actions")
Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Link: https://lore.kernel.org/bpf/159410593992.1093222.90072558386094370.stgit@firesoul