kernel - Fix memory leak, clean up kernel slab fragmentation
* The kernel slab allocator collects off-cpu kfree()s in z_RChunks. This
linked list is freed up by the owning cpu. However, zones which are not
at the head of the list can wind up with non-NULL z_RChunks which never
get freed.
* Add a 10-second callout on every cpu to clean-up these stale zones, giving
the kernel a chance to free the related zones.
* This was probably the cause for other kernel memory leaks reported in the
past.
Found-by: sephe