netfilter: ipset: Add list flush to cancel_gc

netfilter: ipset: Add list flush to cancel_gc

Origin: https://git.kernel.org/linus/c1193d9bbbd379defe9be3c6de566de684de8a6f

Flushing list in cancel_gc drops references to other lists right away,
without waiting for RCU to destroy list. Fixes race when referenced
ipsets can't be destroyed while referring list is scheduled for destroy.

Fixes: 97f7cf1cd80e ("netfilter: ipset: fix performance regression in swap operation")
Signed-off-by: Alexander Maltsev <keltar.gw@gmail.com>
Acked-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Gbp-Pq: Topic bugfix/all
Gbp-Pq: Name netfilter-ipset-Add-list-flush-to-cancel_gc.patch