chg: dev: Convert slabtop and slabheader to use the cds list

This is the first MR in series that aims to reduce the node locking
by replacing the single-linked list of slabtop(s) and slabheader(s)
with CDS linked list.  This commit doesn't do anything else beyond
replacing .next and .down links with the cds_list_head.  The RCU
semantics will be added later.

Merge branch 'ondrej/use-rcu-list-for-slabtop' into 'main'

See merge request isc-projects/bind9!10944