netfilter: nf_tables: skip transaction if update object is not implemented

Turn update into noop as a follow up for:

  9fedd894 ("netfilter: nf_tables: fix unexpected EOPNOTSUPP error")

instead of adding a transaction object which is simply discarded at a
later stage of the commit protocol.
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -7776,6 +7776,9 @@ static int nf_tables_newobj(struct sk_buff *skb, const struct nfnl_info *info,
 		if (WARN_ON_ONCE(!type))
 			return -ENOENT;
 
+		if (!obj->ops->update)
+			return 0;
+
 		nft_ctx_init(&ctx, net, skb, info->nlh, family, table, NULL, nla);
 
 		return nf_tables_updobj(&ctx, type, nla[NFTA_OBJ_DATA], obj);
@@ -9467,9 +9470,10 @@ static void nft_obj_commit_update(struct nft_trans *trans)
 	obj = nft_trans_obj(trans);
 	newobj = nft_trans_obj_newobj(trans);
 
-	if (obj->ops->update)
-		obj->ops->update(obj, newobj);
+	if (WARN_ON_ONCE(!obj->ops->update))
+		return;
 
+	obj->ops->update(obj, newobj);
 	nft_obj_destroy(&trans->ctx, newobj);
 }