LU-16992 kfilnd: Expand debugfs to record min/max

LU-16992 kfilnd: Expand debugfs to record min/max

This will be useful in determining how long kfilnd transactions take
when underlying NIC gets congested.

Test-Parameters: trivial
HPE-bug-id: LUS-11497
Signed-off-by: Ian Ziemba <ian.ziemba@hpe.com>
Change-Id: I5506329086e6284e04ec7b609485d582a35ca0b5
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/51784
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Ron Gredvig <ron.gredvig@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>