selftests/futex: Fix some futex_numa_mpol subtests

selftests/futex: Fix some futex_numa_mpol subtests

The "Memory out of range" subtest of futex_numa_mpol assumes that memory
access outside of the mmap'ed area is invalid. That may not be the case
depending on the actual memory layout of the test application. When that
subtest was run on an x86-64 system with latest upstream kernel, the test
passed as an error was returned from futex_wake(). On another PowerPC system,
the same subtest failed because futex_wake() returned 0.

  Bail out! futex2_wake(64, 0x86) should fail, but didn't

Looking further into the passed subtest on x86-64, it was found that an
-EINVAL was returned instead of -EFAULT. The -EINVAL error was returned
because the node value test with FLAGS_NUMA set failed with a node value
of 0x7f7f. IOW, the futex memory was accessible and futex_wake() failed
because the supposed node number wasn't valid. If that memory location
happens to have a very small value (e.g. 0), the test will pass and no
error will be returned.

Since this subtest is non-deterministic, drop it unless a guard page beyond
the mmap region is explicitly set.

The other problematic test is the "Memory too small" test. The futex_wake()
function returns the -EINVAL error code because the given futex address isn't
8-byte aligned, not because only 4 of the 8 bytes are valid and the other
4 bytes are not. So change the name of this subtest to "Mis-aligned futex" to
reflect the reality.

  [ bp: Massage commit message. ]

Fixes: 3163369407ba ("selftests/futex: Add futex_numa_mpol")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Borislav Petkov (AMD) <bp@alien8.de>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://lore.kernel.org/20250827130011.677600-3-bigeasy@linutronix.de