overlay/026: Fix test expectation for newer kernels

overlay/026: Fix test expectation for newer kernels

The test checks the expectaion from old kernels that set/get of
trusted.overlay.* xattrs is not supported on an overlayfs filesystem.

New kernels support set/get xattr of trusted.overlay.* xattrs, so adapt
the test to check that either both set and get work on new kernel, or
neither work on old kernel.

Signed-off-by: Alexander Larsson <alexl@redhat.com>
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Reviewed-by: Zorro Lang <zlang@redhat.com>
Signed-off-by: Zorro Lang <zlang@kernel.org>