http_async_client: use literal module name for stats group

- prevent conflicts with global exports

src/modules/http_async_client/http_async_client_mod.c

@@ -232,7 +232,7 @@ static int mod_init(void)
 
 #ifdef STATISTICS
 	/* register statistics */
-	if(register_module_stats(exports.name, mod_stats) != 0) {
+	if(register_module_stats("http_async_client", mod_stats) != 0) {
 		LM_ERR("failed to register core statistics\n");
 		return -1;
 	}