Cleanup usage of LINUX_VERSION_CODE for older kernels

Cleanup usage of LINUX_VERSION_CODE for older kernels

2.6.18 is the minimum supported linux kernel level. There are
preprocessor checks for specific kernel versions that predate 2.6.18.

Refactor the use of the LINUX_VERSION_CODE that checks for kernel
versions older than 2.6.18.

In addition, there are a couple of locations where the kernel version
is checked with an additional test to see if module_param or
module_param_array are defined.  These checks are used to determine
whether to use the macros module_param/module_param_array or to use
the macro MODULE_PARM. The macros module_param and module_param_array
were present in Linux prior to 2.6.12.  The macro MODULE_PARM was marked
as deprecated prior to 2.6.12 and removed in Linux 2.6.17 (8d3b33f67fd
'[PATCH] Remove MODULE_PARM').

Remove the preprocessor checks for module_param/module_param_array and
remove the use of MODULE_PARM.

The updates should have no functional changes.

Change-Id: I1dc5dca1252abfc865917757989df235c75059a6
Reviewed-on: https://gerrit.openafs.org/14389
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>