netfilter: nftables: report EOPNOTSUPP on unsupported flowtable flags

Error was not set accordingly.

Fixes: 8bb69f3b ("netfilter: nf_tables: add flowtable offload control plane")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -6963,8 +6963,10 @@ static int nf_tables_newflowtable(struct net *net, struct sock *nlsk,
 	if (nla[NFTA_FLOWTABLE_FLAGS]) {
 		flowtable->data.flags =
 			ntohl(nla_get_be32(nla[NFTA_FLOWTABLE_FLAGS]));
-		if (flowtable->data.flags & ~NFT_FLOWTABLE_MASK)
+		if (flowtable->data.flags & ~NFT_FLOWTABLE_MASK) {
+			err = -EOPNOTSUPP;
 			goto err3;
+		}
 	}
 
 	write_pnet(&flowtable->data.net, net);