mm, slab: ignore hardened usercopy parameters when disabled

With CONFIG_HARDENED_USERCOPY not enabled, there are no
__check_heap_object() checks happening that would use the struct
kmem_cache useroffset and usersize fields. Yet the fields are still
initialized, preventing merging of otherwise compatible caches.

Also the fields contribute to struct kmem_cache size unnecessarily when
unused. Thus #ifdef them out completely when CONFIG_HARDENED_USERCOPY is
disabled. In kmem_dump_obj() print object_size instead of usersize, as
that's actually the intention.

In a quick virtme boot test, this has reduced the number of caches in
/proc/slabinfo from 131 to 111.

Cc: Kees Cook <[email protected]>
Signed-off-by: Vlastimil Babka <[email protected]>
Acked-by: Roman Gushchin <[email protected]>
Acked-by: Mike Rapoport <[email protected]>
Reviewed-by: Christoph Lameter <[email protected]>

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