LU-16563 tests: Check peer NI health after link down

LU-16563 tests: Check peer NI health after link down

Validate whether peer NI health is decremented when a link is downed.

Test-Parameters: trivial testlist=sanity-lnet env=ONLY=303
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I5aa4a2f6efa2c0be2d7eb166b21ffab268e39941
Reviewed-on: https://review.whamcloud.com/c/fs/lustre-release/+/50188
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Cyril Bordage <cbordage@whamcloud.com>
Reviewed-by: Frank Sehr <fsehr@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>