LU-12646 lnet: Prefer route specified by rtr_nid

LU-12646 lnet: Prefer route specified by rtr_nid

Restore an optimization that was initially added under LU-11413. For
routed REPLY and ACK we should preferably use the same router from
which the GET/PUT was receieved.

Cray-bug-id: LUS-8008
Test-Parameters: trivial
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ia3059cddf70e1c477d90acdd90c13b4c5a292f4f
Reviewed-on: https://review.whamcloud.com/35737
Tested-by: jenkins <devops@whamcloud.com>
Reviewed-by: Alexandr Boyko <c17825@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <stancheff@cray.com>
Reviewed-by: Neil Brown <neilb@suse.de>
Reviewed-by: Oleg Drokin <green@whamcloud.com>