netfilter: add __rcu annotations

Add some __rcu annotations and use helpers to reduce number of sparse
warnings (CONFIG_SPARSE_RCU_POINTER=y)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Signed-off-by: Patrick McHardy <kaber@trash.net>
diff --git a/net/netfilter/nf_log.c b/net/netfilter/nf_log.c
index b07393e..20c775c 100644
--- a/net/netfilter/nf_log.c
+++ b/net/netfilter/nf_log.c
@@ -161,7 +161,8 @@
 	struct nf_logger *t;
 	int ret;
 
-	logger = nf_loggers[*pos];
+	logger = rcu_dereference_protected(nf_loggers[*pos],
+					   lockdep_is_held(&nf_log_mutex));
 
 	if (!logger)
 		ret = seq_printf(s, "%2lld NONE (", *pos);
@@ -249,7 +250,8 @@
 		mutex_unlock(&nf_log_mutex);
 	} else {
 		mutex_lock(&nf_log_mutex);
-		logger = nf_loggers[tindex];
+		logger = rcu_dereference_protected(nf_loggers[tindex],
+						   lockdep_is_held(&nf_log_mutex));
 		if (!logger)
 			table->data = "NONE";
 		else