selftests: xsk: fix reporting of failed tests

Fix the reporting of failed tests as it was broken in several
ways. First, a failed test was reported as both failed and passed
messing up the count. Second, tests were not aborted after a failure
and could generate more "failures" messing up the count even
more. Third, the failure reporting from the application to the shell
script was wrong. It always reported pass. And finally, the handling
of the failures in the launch script was not correct.

Correct all this by propagating the failure up through the function
calls to a calling function that can abort the test. A receiver or
sender thread will mark the new variable in the test spec called fail,
if a test has failed. This is then picked up by the main thread when
everyone else has exited and this is then marked and propagated up to
the calling script.

Also add a summary function in the calling script so that a user
does not have to go through the sub tests to see if something has
failed.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20220510115604.8717-5-magnus.karlsson@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>