LU-6142 contrib: update checkpatch.pl to 6.10-rc2

LU-6142 contrib: update checkpatch.pl to 6.10-rc2

checkpatch.pl hasn't been updated in around 7 years. To make sure
we don't waste our efforts, update the script while porting a few
Lustre specific changes.

This updates checkpatch.pl to 6.10-rc2 while recording the changes
in contrib/.

This is mostly a simple port of the old changes to a new version of
checkpatch.pl. It is intended to silence a few false positives and
generate a few Lustre specific warnings.

One feature has been added: the ability to differentiate between
user space code and kernel code when doing spell checks.

I tested this by running the updated script across the entire tree,
ensuring that nothing failed:

contrib:         loc=192    errors/warnings=1
libcfs:          loc=25117  errors/warnings=1624
lnet:            loc=133290 errors/warnings=16381
lustre:          loc=645087 errors/warnings=81360

Also, add a userspace_spelling.txt file by copying spelling.txt. We
start by simply duplicating the old spelling.txt file while removing
a number of entries.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: Ia39c7f04d2407786f158d7f6f95968e182e99ebf
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/54153
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>