configure: --with-linux-kernel-packaging should default to disabled

configure: --with-linux-kernel-packaging should default to disabled

the test for this build feature is reversed.  by default, the value for
with_linux_kernel_packaging will not be defined which makes the existing
test pick MPS='SP' instead of LINUX_WHICH_MODULES.  based on the configure
help messages, this would appear to be an opt-in not an opt-out.

...
Optional Packages:
...
  --with-linux-kernel-packaging
                          use standard naming conventions to aid Linux kernel
                          build packaging (disables MPS, sets the kernel
                          module name to openafs.ko, and installs kernel
                          modules into the standard Linux location)
...

Change-Id: Ie16fba165e6c85b7ecbce887badb9ffc06a3a7a8
Reviewed-on: http://gerrit.openafs.org/2869
Reviewed-by: Simon Wilkinson <sxw@inf.ed.ac.uk>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: BuildBot <buildbot@rampaginggeek.com>