selftests/xsx: test for huge pages only once

selftests/xsx: test for huge pages only once

Test for hugepages only once at the beginning of the execution of the
whole test suite, instead of before each test that needs huge
pages. These are the tests that use unaligned mode. As more unaligned
tests will be added, so the current system just does not scale.

With this change, there are now three possible outcomes of a test run:
fail, pass, or skip. To simplify the handling of this, the function
testapp_validate_traffic() now returns this value to the main loop. As
this function is used by nearly all tests, it meant a small change to
most of them.

Signed-off-by: Magnus Karlsson <magnus.karlsson@intel.com>
Link: https://lore.kernel.org/r/20230516103109.3066-8-magnus.karlsson@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>