mm/kasan/kunit: extend vmalloc OOB tests to cover vrealloc()

mm/kasan/kunit: extend vmalloc OOB tests to cover vrealloc()

Extend the vmalloc_oob() test to validate OOB detection after resizing
vmalloc allocations with vrealloc().

The test now verifies that KASAN correctly poisons and unpoisons vmalloc
memory when allocations are shrunk and expanded, ensuring OOB accesses are
reliably detected after each resize.

[ryabinin.a.a@gmail.com: adjust vrealloc() size]
Link: https://lkml.kernel.org/r/20260116132822.22227-1-ryabinin.a.a@gmail.com
Link: https://lkml.kernel.org/r/20260113191516.31015-2-ryabinin.a.a@gmail.com
Signed-off-by: Andrey Ryabinin <ryabinin.a.a@gmail.com>
Reviewed-by: Andrey Konovalov <andreyknvl@gmail.com>
Cc: Alexander Potapenko <glider@google.com>
Cc: Dmitriy Vyukov <dvyukov@google.com>
Cc: Maciej Żenczykowski <maze@google.com>
Cc: Uladzislau Rezki <urezki@gmail.com>
Cc: Vincenzo Frascino <vincenzo.frascino@arm.com>
Cc: Maciej Wieczor-Retman <maciej.wieczor-retman@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>