netfilter: nft_dynset: do not reject set updates with NFT_SET_EVAL

NFT_SET_EVAL is signalling the kernel that this sets can be updated from
the evaluation path, even if there are no expressions attached to the
element. Otherwise, set updates with no expressions fail. Update
description to describe the right semantics.

Fixes: 22fe54d5fefc ("netfilter: nf_tables: add support for dynamic set updates")
Signed-off-by: Pablo Neira Ayuso <[e-mail]>

include/uapi/linux/netfilter/nf_tables.h

···
  * @NFT_SET_INTERVAL: set contains intervals
  * @NFT_SET_MAP: set is used as a dictionary
  * @NFT_SET_TIMEOUT: set uses timeouts
- * @NFT_SET_EVAL: set contains expressions for evaluation
+ * @NFT_SET_EVAL: set can be updated from the evaluation path
  * @NFT_SET_OBJECT: set contains stateful objects
  */
 enum nft_set_flags {

net/netfilter/nft_dynset.c

···
 				goto err1;
 			set->ops->gc_init(set);
 		}
-
-	} else if (set->flags & NFT_SET_EVAL)
-		return -EINVAL;
+	}
 
 	nft_set_ext_prepare(&priv->tmpl);
 	nft_set_ext_add_length(&priv->tmpl, NFT_SET_EXT_KEY, set->klen);