netfilter: nf_tables: relax NFTA_SET_ELEM_KEY_END set flags requirements

Otherwise EINVAL is bogusly reported to userspace when deleting a set
element. NFTA_SET_ELEM_KEY_END does not need to be set in case of:

- insertion: if not present, start key is used as end key.
- deletion: only start key needs to be specified, end key is ignored.

Hence, relax the sanity check.

Fixes: 88cccd9 ("netfilter: nf_tables: NFTA_SET_ELEM_KEY_END requires concat and interval flags")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

Author: ummakynes

net/netfilter/nf_tables_api.c

@@ -5865,8 +5865,9 @@ static bool nft_setelem_valid_key_end(const struct nft_set *set,
 			  (NFT_SET_CONCAT | NFT_SET_INTERVAL)) {
 		if (flags & NFT_SET_ELEM_INTERVAL_END)
 			return false;
-		if (!nla[NFTA_SET_ELEM_KEY_END] &&
-		    !(flags & NFT_SET_ELEM_CATCHALL))
+
+		if (nla[NFTA_SET_ELEM_KEY_END] &&
+		    flags & NFT_SET_ELEM_CATCHALL)
 			return false;
 	} else {
 		if (nla[NFTA_SET_ELEM_KEY_END])