LU-12763 lnet: Use alternate ping processing for non-mr peers

LU-12763 lnet: Use alternate ping processing for non-mr peers

Router peers without multi-rail capabilities (i.e. older Lustre
versions) or router peers that have discovery disabled need to use
the alternate ping processing introduced by LU-12422. Otherwise,
these peers go through the normal discovery processing, but their
remote network interfaces are never added to the peer object. This
causes routes through these peers to be considered down when
avoid_asym_router_failure is enabled.

Cray-bug-id: LUS-7866
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ib567b66c871abdad9b39b4f29b38eca424d4cd8d
Reviewed-on: https://review.whamcloud.com/36182
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>