geneve: Unregister pernet subsys on module unload.

The pernet ops aren't ever unregistered, which causes a memory
leak and an OOPs if the module is ever reinserted.

Fixes: 0b5e8b8eeae4 ("net: Add Geneve tunneling protocol driver")
CC: Andy Zhou <azhou@nicira.com>
Signed-off-by: Jesse Gross <jesse@nicira.com>
Acked-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/geneve.c

@@ -366,6 +366,7 @@ late_initcall(geneve_init_module);
 static void __exit geneve_cleanup_module(void)
 {
 	destroy_workqueue(geneve_wq);
+	unregister_pernet_subsys(&geneve_net_ops);
 }
 module_exit(geneve_cleanup_module);