netfilter: nf_tables: defer all object release via rcu

Now that all objects are released in the reverse order via the
transaction infrastructure, we can enqueue the release via
call_rcu to save one synchronize_rcu. For small rule-sets loaded
via nft -f, it now takes around 50ms less here.

Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

include/net/netfilter/nf_tables.h

@@ -393,12 +393,14 @@ struct nft_rule {
 /**
  *	struct nft_trans - nf_tables object update in transaction
  *
+ *	@rcu_head: rcu head to defer release of transaction data
  *	@list: used internally
  *	@msg_type: message type
  *	@ctx: transaction context
  *	@data: internal information related to the transaction
  */
 struct nft_trans {
+	struct rcu_head			rcu_head;
 	struct list_head		list;
 	int				msg_type;
 	struct nft_ctx			ctx;