netfilter: ipset: Fix subcounter update skip

If IPSET_FLAG_SKIP_SUBCOUNTER_UPDATE is set, user requested to not
update counters in sub sets. Therefore IPSET_FLAG_SKIP_COUNTER_UPDATE
must be set, not unset.

Fixes: 6e01781d ("netfilter: ipset: set match: add support to match the counters")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>