In ip_set_match_extensions(), for sets with counters, we take care of
updating counters themselves by calling ip_set_update_counter(), and of
checking if the given comparison and values match, by calling
ip_set_match_counter() if needed.

However, if a given comparison on counters doesn't match the configured
values, that doesn't mean the set entry itself isn't matching.

This fix restores the behaviour we had before commit 4750005a
("netfilter: ipset: Fix "don't update counters" mode when counters used
at the matching"), without reintroducing the issue fixed there: back
then, mtype_data_match() first updated counters in any case, and then
took care of matching on counters.

Now, if the IPSET_FLAG_SKIP_COUNTER_UPDATE flag is set,
ip_set_update_counter() will anyway skip counter updates if desired.

The issue observed is illustrated by this reproducer:

  ipset create c hash:ip counters
  ipset add c 192.0.2.1
  iptables -I INPUT -m set --match-set c src --bytes-gt 800 -j DROP

if we now send packets from 192.0.2.1, bytes and packets counters
for the entry as shown by 'ipset list' are always zero, and, no
matter how many bytes we send, the rule will never match, because
counters themselves are not updated.

Reported-by: Mithil Mhatre <mmhatre@redhat.com>
Fixes: 4750005a ("netfilter: ipset: Fix "don't update counters" mode when counters used at the matching")
Signed-off-by: Stefano Brivio <sbrivio@redhat.com>
Signed-off-by: Jozsef Kadlecsik <kadlec@netfilter.org>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>