netfilter: nf_tables: do not dump chain counters if not enabled

Chain counters are only enabled on demand since 9f08ea84, skip them
when dumping them via netlink.

Fixes: 9f08ea84 ("netfilter: nf_tables: keep chain counters away from hot path")
Reported-by: NJohny Mattsson <johny.mattsson+kernel@gmail.com>
Tested-by: NJohny Mattsson <johny.mattsson+kernel@gmail.com>
Signed-off-by: NPablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -1048,7 +1048,7 @@ static int nf_tables_fill_chain_info(struct sk_buff *skb, struct net *net,
 		if (nla_put_string(skb, NFTA_CHAIN_TYPE, basechain->type->name))
 			goto nla_put_failure;
 
-		if (nft_dump_stats(skb, nft_base_chain(chain)->stats))
+		if (basechain->stats && nft_dump_stats(skb, basechain->stats))
 			goto nla_put_failure;
 	}