LU-16002 ptlrpc: adds configurable ping interval

LU-16002 ptlrpc: adds configurable ping interval

The patch adds ability to change ping interval and eviction
mutliplier. A default values stay as before.
Example
lctl set_param ping_interval=10
lctl set_param evict_multiplier=5

HPE-bug-id: LUS-11054
Signed-off-by: Alexander Boyko <alexander.boyko@hpe.com>
Change-Id: I012dc7ba28ce9ff3edf0f145a403679bfaebbf55
Reviewed-on: https://review.whamcloud.com/47982
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Sergey Cheremencev <sergey.cheremencev@hpe.com>
Reviewed-by: Alexander Zarochentsev <alexander.zarochentsev@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>