where "m" is number of source nodes and "n" is number of states. Thus,
on heavy loaded router its processing consumed a lot of CPU time.
Reimplement it with O(m+n) complexity. We first scan through source
nodes and disconnect matching ones, putting them on the freelist and
marking with a cookie value in their expire field. Then we scan through
the states, detecting references to source nodes with a cookie, and
disconnect them as well. Then the freelist is passed to pf_free_src_nodes().
In collaboration with: Kajetan Staszkiewicz <kajetan.staszkiewicz innogames.de>
PR: kern/176763
Sponsored by: InnoGames GmbH
Sponsored by: Nginx, Inc.
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