netfilter: nf_log: replace BUG_ON by WARN_ON_ONCE when putting logger

Module reference is bumped for each user, this should not ever happen.

But BUG_ON check should use rcu_access_pointer() instead.

If this ever happens, do WARN_ON_ONCE() instead of BUG_ON() and
consolidate pointer check under the rcu read side lock section.

Fixes: fab4085f ("netfilter: log: nf_log_packet() as real unified interface")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_log.c

@@ -193,11 +193,12 @@ void nf_logger_put(int pf, enum nf_log_type type)
 		return;
 	}
 
-	BUG_ON(loggers[pf][type] == NULL);
-
 	rcu_read_lock();
 	logger = rcu_dereference(loggers[pf][type]);
-	module_put(logger->me);
+	if (!logger)
+		WARN_ON_ONCE(1);
+	else
+		module_put(logger->me);
 	rcu_read_unlock();
 }
 EXPORT_SYMBOL_GPL(nf_logger_put);