sysfs: Allow mounting without CONFIG_NET

In kobj_ns_current_may_mount the default should be to allow the mount.
The test is only for a single kobj_ns_type at a time, and unless there
is a reason to prevent it the mounting sysfs should be allowed.
Subsystems that are not registered can't have are not involved so can't
have a reason to prevent mounting sysfs.

This is a bug-fix to commit 7dc5dbc ("sysfs: Restrict mounting
sysfs") that came in via the userns tree during the 3.12 merge window.

Reported-and-tested-by: James Hogan <james.hogan@imgtec.com>
Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

lib/kobject.c

@@ -933,10 +933,7 @@ const struct kobj_ns_type_operations *kobj_ns_ops(struct kobject *kobj)
 
 bool kobj_ns_current_may_mount(enum kobj_ns_type type)
 {
-	bool may_mount = false;
-
-	if (type == KOBJ_NS_TYPE_NONE)
-		return true;
+	bool may_mount = true;
 
 	spin_lock(&kobj_ns_type_lock);
 	if ((type > KOBJ_NS_TYPE_NONE) && (type < KOBJ_NS_TYPES) &&