LU-16518 lnet: fix implicit-fallthrough warnings

LU-16518 lnet: fix implicit-fallthrough warnings

Explicitly lable switch-case intentional fallthroughs
and reorder cases as needed to silence implicit-fallthrough
warnings as reported by Clang.

Test-Parameters: trivial
Signed-off-by: Timothy Day <timday@amazon.com>
Change-Id: If6550d97e9f49a6722f8e9a2ae34ba2338f39e73
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/58349
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Chris Horn <chris.horn@hpe.com>
Reviewed-by: James Simmons <jsimmons@infradead.org>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>