netfilter: nft_connlimit: update the count if add was skipped

netfilter: nft_connlimit: update the count if add was skipped

Connlimit expression can be used for all kind of packets and not only
for packets with connection state new. See this ruleset as example:

table ip filter {
        chain input {
                type filter hook input priority filter; policy accept;
                tcp dport 22 ct count over 4 counter
        }
}

Currently, if the connection count goes over the limit the counter will
count the packets. When a connection is closed, the connection count
won't decrement as it should because it is only updated for new
connections due to an optimization on __nf_conncount_add() that prevents
updating the list if the connection is duplicated.

To solve this problem, check whether the connection was skipped and if
so, update the list. Adjust count_tree() too so the same fix is applied
for xt_connlimit.

Fixes: 976afca1ceba ("netfilter: nf_conncount: Early exit in nf_conncount_lookup() and cleanup")
Closes: https://lore.kernel.org/netfilter/trinity-85c72a88-d762-46c3-be97-36f10e5d9796-1761173693813@3c-app-mailcom-bs12/
Signed-off-by: Fernando Fernandez Mancera <fmancera@suse.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>