selftests/bpf: make correct use of exit codes in bpf selftests

The selftests depend on using the shell exit code as a mean of
detecting the success or failure of test-binary executed.  The
appropiate output "[PASS]" or "[FAIL]" in generated by
tools/testing/selftests/lib.mk.

Notice that the exit code is masked with 255. Thus, be careful if
using the number of errors as the exit code, as 256 errors would be
seen as a success.

There are two standard defined exit(3) codes:
 /usr/include/stdlib.h
 #define EXIT_FAILURE    1       /* Failing exit status.  */
 #define EXIT_SUCCESS    0       /* Successful exit status.  */

Fix test_verifier.c to not use the negative value of variable
"results", but instead return EXIT_FAILURE.

Fix test_align.c and test_progs.c to actually use exit codes, before
they were always indicating success regardless of results.

Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>