Linux: include kthread.h before afs includes

Linux: include kthread.h before afs includes

We need to include kthread.h before the afs standard includes
to avoid clashing with the printf -> printk mapping.

Reviewed-on: http://gerrit.openafs.org/7988
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
(cherry picked from commit 8b6926e43f31a30a95e5883fd4b9e72924b3371d)

Change-Id: I0dbb696e3af5172c9a72d183f2acd10107bedcf5
Reviewed-on: http://gerrit.openafs.org/8605
Reviewed-by: Paul Smeddle <paul.smeddle@gmail.com>
Tested-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: BuildBot <buildbot@rampaginggeek.com>