Merge branch 'netlink-add-nftables-spec-w-multi-messages'

Donald Hunter says:

====================
netlink: Add nftables spec w/ multi messages

This series adds a ynl spec for nftables and extends ynl with a --multi
command line option that makes it possible to send transactional batches
for nftables.

This series includes a patch for nfnetlink which adds ACK processing for
batch begin/end messages. If you'd prefer that to be sent separately to
nf-next then I can do so, but I included it here so that it gets seen in
context.

An example of usage is:

./tools/net/ynl/cli.py \
 --spec Documentation/netlink/specs/nftables.yaml \
 --multi batch-begin '{"res-id": 10}' \
 --multi newtable '{"name": "test", "nfgen-family": 1}' \
 --multi newchain '{"name": "chain", "table": "test", "nfgen-family": 1}' \
 --multi batch-end '{"res-id": 10}'
[None, None, None, None]

It can also be used for bundling get requests:

./tools/net/ynl/cli.py \
 --spec Documentation/netlink/specs/nftables.yaml \
 --multi gettable '{"name": "test", "nfgen-family": 1}' \
 --multi getchain '{"name": "chain", "table": "test", "nfgen-family": 1}' \
 --output-json
[{"name": "test", "use": 1, "handle": 1, "flags": [],
 "nfgen-family": 1, "version": 0, "res-id": 2},
 {"table": "test", "name": "chain", "handle": 1, "use": 0,
 "nfgen-family": 1, "version": 0, "res-id": 2}]

There are 2 issues that may be worth resolving:

 - ynl reports errors by raising an NlError exception so only the first
   error gets reported. This could be changed to add errors to the list
   of responses so that multiple errors could be reported.

 - If any message does not get a response (e.g. batch-begin w/o patch 2)
   then ynl waits indefinitely. A recv timeout could be added which
   would allow ynl to terminate.
====================

Link: https://lore.kernel.org/r/20240418104737.77914-1-donald.hunter@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>