Refactor afs_ioctl code

Refactor afs_ioctl code

The ioctl code was a nightmare of #ifdefs. This patch reworks it
so that there is a single function for each operating system, which
makes it much easier to see what's going on. Eventually it should be
possible to move these reworked functions out into the osi directories

Change-Id: I61f70b23ad0c7ea137e6aa843be6f75c83c02843
Reviewed-on: http://gerrit.openafs.org/1244
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>