netfilter: nf_tables: missing error reporting for not selected expressions

Sometimes users forget to turn on nftables extensions from Kconfig that
they need. In such case, the error reporting from userspace is
misleading:

 $ sudo nft add rule x y counter
 Error: Could not process rule: No such file or directory
 add rule x y counter
 ^^^^^^^^^^^^^^^^^^^^

Add missing NL_SET_BAD_ATTR() to provide a hint:

 $ nft add rule x y counter
 Error: Could not process rule: No such file or directory
 add rule x y counter
              ^^^^^^^

Fixes: 83d9dcba ("netfilter: nf_tables: extended netlink error reporting for expressions")
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

net/netfilter/nf_tables_api.c

@@ -3328,8 +3328,10 @@ static int nf_tables_newrule(struct sk_buff *skb, const struct nfnl_info *info,
 			if (n == NFT_RULE_MAXEXPRS)
 				goto err1;
 			err = nf_tables_expr_parse(&ctx, tmp, &expr_info[n]);
-			if (err < 0)
+			if (err < 0) {
+				NL_SET_BAD_ATTR(extack, tmp);
 				goto err1;
+			}
 			size += expr_info[n].ops->size;
 			n++;
 		}