mm, slab: clean up slab->obj_exts always

In the Linux kernel, the following vulnerability has been resolved:

mm, slab: clean up slab->obj_exts always

When memory allocation profiling is disabled at runtime or due to an

error, shutdown_mem_profiling() is called: slab->obj_exts which

previously allocated remains.

It won't be cleared by unaccount_slab() because of

mem_alloc_profiling_enabled() not true. It's incorrect, slab->obj_exts

should always be cleaned up in unaccount_slab() to avoid following error:

[...]BUG: Bad page state in process...

..

[...]page dumped because: page still charged to cgroup

[[email protected]: fold need_slab_obj_ext() into its only user]