LU-2467 protocol: Add OBD_CONNECT_PINGLESS

LU-2467 protocol: Add OBD_CONNECT_PINGLESS

Reserve a bit for OBD_CONNECT_PINGLESS, which indicates a client is
capable of suppressing keep-alive OBD_PINGs.  If granted by a server,
it means the server does not require (but still allows) pings.

Change-Id: Ie10f505badd4250582656295eac2fd6844bb76b3
Signed-off-by: Li Wei <wei.g.li@intel.com>
Reviewed-on: http://review.whamcloud.com/5232
Tested-by: Hudson
Tested-by: Maloo <whamcloud.maloo@gmail.com>
Reviewed-by: Andreas Dilger <andreas.dilger@intel.com>