xenstore: set correct error code when violating quota

When the number of permitted xenstore entries for a domain is being
exceeded the operation trying to create a new entry is denied.
Unfortunately errno isn't being set in this case so the error code
returned to the client is undefined.

Set errno to ENOSPC in this case.

Signed-off-by: Juergen Gross <jgross@suse.com>
Acked-by: Wei Liu <wei.liu2@citrix.com>

tools/xenstore/xenstored_core.c

@@ -937,8 +937,10 @@ static struct node *construct_node(struct connection *conn, const void *ctx,
 	if (!parent)
 		return NULL;
 
-	if (domain_entry(conn) >= quota_nb_entry_per_domain)
+	if (domain_entry(conn) >= quota_nb_entry_per_domain) {
+		errno = ENOSPC;
 		return NULL;
+	}
 
 	/* Add child to parent. */
 	base = basename(name);