netfilter: nf_tables: store new sets in dedicated list

netfilter: nf_tables: store new sets in dedicated list

nft_set_lookup_byid() is very slow when transaction becomes large, due to
walk of the transaction list.

Add a dedicated list that contains only the new sets.

Before: nft -f ruleset 0.07s user 0.00s system 0% cpu 1:04.84 total
After: nft -f ruleset 0.07s user 0.00s system 0% cpu 30.115 total

.. where ruleset contains ~10 sets with ~100k elements.
The above number is for a combined flush+reload of the ruleset.

With previous flush, even the first NEWELEM has to walk through a few
hundred thousands of DELSET(ELEM) transactions before the first NEWSET
object. To cope with random-order-newset-newsetelem we'd need to replace
commit_set_list with a hashtable.

Expectation is that a NEWELEM operation refers to the most recently added
set, so last entry of the dedicated list should be the set we want.

NB: This is not a bug fix per se (functionality is fine), but with
larger transaction batches list search takes forever, so it would be
nice to speed this up for -stable too, hence adding a "fixes" tag.

Fixes: 958bee14d071 ("netfilter: nf_tables: use new transaction infrastructure to handle sets")
Reported-by: Nadia Pinaeva <n.m.pinaeva@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>