Linux 3.17: No more typedef for ctl_table

The typedef has been removed so we need to use the structure
directly.

Note that the API for register_sysctl_table has also changed
with 3.17, but it reverted back to a form that existed
before and the configure tests handle it correctly.

Reviewed-on: http://gerrit.openafs.org/11455
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: D Brashear <shadow@your-file-system.com>
(cherry picked from commit 6a23ca5b6e8bcaf881be7a4c50bfba72d001e6cd)

Change-Id: Ifb8fc0b9b01d2578c65407608f0e1b3f3b254459
Reviewed-on: http://gerrit.openafs.org/11549
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>