LU-13569 lnet: Recover peer NI w/exponential backoff interval

LU-13569 lnet: Recover peer NI w/exponential backoff interval

Perform LNet recovery pings of peer NIs with an exponential backoff
interval.
 - The interval is equal to 2^(number failed pings) up to a maximum
   of 900 seconds (15 minutes).
 - When a message is received the count of failed pings for the
   associated peer NI is reset to 0 so that recovery can happen more
   quickly.

Test-Parameters: trivial
HPE-bug-id: LUS-9109
Signed-off-by: Chris Horn <chris.horn@hpe.com>
Change-Id: Ic7e60455015a0236a96010c07fc0ddd02078cf92
Reviewed-on: https://review.whamcloud.com/39720
Reviewed-by: Neil Brown <neilb@suse.de>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>