LU-13569 lnet: Add health ping stats

Add the NI and peer NI ping count and next ping timestamp to
detailed output of lnetctl peer and net output.

Test-Parameters: trivial
HPE-bug-id: LUS-9109
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: I208cb3ea0b08a2984572cf0ec9874dbd09f6168e
Reviewed-on: https://review.whamcloud.com/40314
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>