LU-9633 mgc: Add kernel doc style for mgc/mgc_request.c

LU-9633 mgc: Add kernel doc style for mgc/mgc_request.c

This patch converts existing functional comments
to kernel doc style comments and removes '/**' for
comments which is not meant to be a kernel-doc comment

Test-Parameters: trivial
Signed-off-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Change-Id: I0b498281acd9f5d5f48f02d436e2add8df4021ae
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58417
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Petros Koutoupis <petros.koutoupis@hpe.com>
Reviewed-by: Anjus George <georgea@ornl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>