LU-13274 uapi: make lnet UAPI headers C99 compliant

LU-13274 uapi: make lnet UAPI headers C99 compliant

Attempting to compile strict C99 user land applications or
libraries with the Lustre UAPI headers will fail. These same
errors can be seen by enabling CONFIG_UAPI_HEADER_TEST as well.
Update the LNet UAPI headers to be compilable with -std=c99.
Add LNet test covering UAPI header handling.

Test-Parameters: trivial testlist=sanity-lnet

Change-Id: Ic1c30ed2d4d9d1d7f11b657d3817a05161367e13
Signed-off-by: James Simmons <jsimmons@infradead.org>
Reviewed-on: https://review.whamcloud.com/37971
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>