Linux: Refactor test for 32bit compat

Linux: Refactor test for 32bit compat

Refactor the preprocessor checks for determining the method to test for
32bit compatibility (64bit kernel performing work for a 32bit task) into
a common inline function, 'afs_in_compat_syscall' that is defined in
LINUX/osi_machdep.h.  Update osi_ioctl.c and afs_syscall.c to use
afs_in_compat_syscall.

Add include afs/sysincludes into osi_machdep.h to ensure linux/compat.h
is pulled for the functions called in afs_in_compat_syscall.

Change-Id: I6610cc19fedd909de8e8941ded05ed1608e52403
Reviewed-on: https://gerrit.openafs.org/14500
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Andrew Deason <adeason@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>