Driver-core: Always create class directories for classses that support namespaces.

This fixes the regression in 2.6.35-rcX where bluetooth network devices
would fail to be deleted from sysfs, causing their destruction and
recreation to fail.  In addition this fixes the mac80211_hwsim driver
where it would leave around sysfs files when the driver was removed.

This problem is discussed at
  https://bugzilla.kernel.org/show_bug.cgi?id=16257



The reason for the regression is that the network namespace support
added to sysfs expects and requires that network devices be put in
directories that can contain only network devices.

Today get_device_parent almost provides that guarantee for all class
devices, except for a specific exception when the parent of a class
devices is a class device.  It would be nice to simply remove that
arguably incorrect special case, but apparently the input devices depend
on it being there.  So I have only removed it for class devices with
network namespace support.  Which today are the network devices.

It has been suggested that a better fix would be to change the parent
device from a class device to a bus device, which in the case of the
bluetooth driver would change /sys/class/bluetooth to /sys/bus/bluetoth,
I can not see how we would avoid significant userspace breakage if we
were to make that change.

Adding an extra directory in the path to the device will also be
userspace visible but it is much less likely to break things.
Everything is still accessible from /sys/class (for example), and it
fixes two bugs.  Adding an extra directory fixes a 3 year old regression
introduced with the new sysfs layout that makes it impossible to rename
bnep0 network devices to names that conflict with hci device attributes
like hci_revsion.  Adding an additional directory removes the new
failure modes introduced by the network namespace code.

If it weren't for the regession in the renaming of network devices I
would figure out how to just make the sysfs code deal with this
configuration of devices.

In summary this patch fixes regressions by changing:
"/sys/class/bluetooth/hci0/bnep0" to "/sys/class/bluetooth/hci0/net/bnep0".

Reported-by: Johannes Berg <johannes@sipsolutions.net>
Reported-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Signed-off-by: Eric W. Biederman <ebiederm@xmission.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>