rhashtable: allow to unload test module

There's no good reason why to disallow unloading of the rhashtable
test case module.

Commit 9d6dbe1b moved the code from a boot test into a stand-alone
module, but only converted the subsys_initcall() handler into a
module_init() function without a related exit handler, and thus
preventing the test module from unloading.

Fixes: 9d6dbe1b ("rhashtable: Make selftest modular")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Thomas Graf <tgraf@suug.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>

lib/test_rhashtable.c

@@ -223,6 +223,11 @@ static int __init test_rht_init(void)
 	return err;
 }
 
+static void __exit test_rht_exit(void)
+{
+}
+
 module_init(test_rht_init);
+module_exit(test_rht_exit);
 
 MODULE_LICENSE("GPL v2");