Enable slab freelist metadata hardening, which in turn enables support
for allocation from separate kmalloc buckets.  The latter is recommended
to be enabled, as per its help text.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/96fc3f0ed509b6364d8aeb297d5acf4abed18404.1722349907.git.geert+renesas@glider.be