selftests/landlock: Test ptrace as much as possible with Yama

selftests/landlock: Test ptrace as much as possible with Yama

Update ptrace tests according to all potential Yama security policies.
This is required to make such tests pass even if Yama is enabled.

Tests are not skipped but they now check both Landlock and Yama boundary
restrictions at run time to keep a maximum test coverage (i.e. positive
and negative testing).

Signed-off-by: Jeff Xu <jeffxu@google.com>
Link: https://lore.kernel.org/r/20230114020306.1407195-2-jeffxu@google.com
Cc: stable@vger.kernel.org
[mic: Add curly braces around EXPECT_EQ() to make it build, and improve
commit message]
Co-developed-by: Mickaël Salaün <mic@digikod.net>
Signed-off-by: Mickaël Salaün <mic@digikod.net>