ns: simplify ns_common_init() further

Simply derive the ns operations from the namespace type.

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Christian Brauner <brauner@kernel.org>

kernel/user_namespace.c

@@ -126,7 +126,7 @@ int create_user_ns(struct cred *new)
 
 	ns->parent_could_setfcap = cap_raised(new->cap_effective, CAP_SETFCAP);
 
-	ret = ns_common_init(ns, &userns_operations);
+	ret = ns_common_init(ns);
 	if (ret)
 		goto fail_free;