mm/sl[au]b: check if large object is valid in __ksize()

mm/sl[au]b: check if large object is valid in __ksize()

If address of large object is not beginning of folio or size of the
folio is too small, it must be invalid. WARN() and return 0 in such
cases.

Cc: Marco Elver <elver@google.com>
Suggested-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Hyeonggon Yoo <42.hyeyoo@gmail.com>
Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>