LU-12756 lnet: Avoid extra lnet_remotenet lookup

LU-12756 lnet: Avoid extra lnet_remotenet lookup

We can keep track of the lnet_remotenet object associated with the
"best" lnet_peer_net, and pass that lnet_remotenet directly to
lnet_find_route_locked().

Test-Parameters: trivial
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ib9808ca885c698ba6c73c5243fbce8b3f499b790
Reviewed-on: https://review.whamcloud.com/36536
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Reviewed-by: Alexey Lyashkov <c17817@cray.com>
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>