LU-13667 ptlrpc: fix endless loop issue

LU-13667 ptlrpc: fix endless loop issue

In ptlrpc_pinger_main, if the process to ping the recoverable
clients or obd_update_maxusage takes too long time, it could
be stuck in endless loop because of the negative value returned
by pinger_check_timeout.

Change-Id: Ib7fc22b3cc31255223bc2be60224ced1a3585f87
Signed-off-by: Hongchao Zhang <hongchao@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/38915
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Olaf Faaland-LLNL <faaland1@llnl.gov>
Reviewed-by: Oleg Drokin <green@whamcloud.com>