LU-13501 lnet: Skip health and resends for single rail configs

LU-13501 lnet: Skip health and resends for single rail configs

If the sender of a message only has a single interface it doesn't
make sense to have LNet track the health of that interface, nor
should it attempt to resend a message when it encounters a local
error. There aren't any alternative interfaces to use for a resend.

Similarly, we needn't track health values of a peer's NIs if the peer
only has a single interface. Nor do we need to attempt to resend
a message to a peer with a single interface. There's an exception for
routers. We rely on NI health to determine route aliveness, so even
if a router only has a single interface we still need to track its
health.

We can use the ln_ping_target to get the count of local NIs, and the
lnet_peer struct already contains a count of the number of peer NIs.

HPE-bug-id: LUS-8826
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Id89159a5d07c1668c1cbdfa9050535380f68d1f6
Reviewed-on: https://review.whamcloud.com/38448
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexander Boyko <alexander.boyko@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>