Linux CM: Use kernel allocator directly

Linux CM: Use kernel allocator directly

In another few locations within the Linux portion of the cache
manager, directly use the kernel allocator. We can do so here
because we can guarantee that the amount of memory being allocated
is less than the page size, and there is a kfree() in all of the
exit paths, so we don't need the magic freeing behaviour, either.

Reviewed-on: http://gerrit.openafs.org/4752
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 7a70c2907b0435653098a611a140fea1ac0b2fac)

Change-Id: I72fd6a2109022af5e14d90ce147705da7ccec587
Reviewed-on: http://gerrit.openafs.org/11933
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Chas Williams <3chas3@gmail.com>
Reviewed-by: Perry Ruiter <pruiter@sinenomine.net>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>