LU-15496 tests: add debugging to sanity/398c

LU-15496 tests: add debugging to sanity/398c

Dump the rpc_stats to help understand why the test is failing.

Test-Parameters: trivial testlist=sanity clientarch=ppc64le env=ONLY=398c,ONLY_REPEAT=100
Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I5ed1b7133eddd242b234a05a670e152e4ca359b7
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/53462
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Arshad Hussain <arshad.hussain@aeoncomputing.com>
Reviewed-by: Jian Yu <yujian@whamcloud.com>
Reviewed-by: Alex Deiter
Reviewed-by: Oleg Drokin <green@whamcloud.com>