LU-13278 lnet: Reconcile discovery push and reply handling

LU-13278 lnet: Reconcile discovery push and reply handling

Reconcile the logic for updating the multi-rail flag of a peer when
processing a discovery PUSH with the logic used when processing a
discovery REPLY.

Cray-bug-id: LUS-8516
Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Idfb4c3729822d03b71f9440ac66176ae6b886022
Reviewed-on: https://review.whamcloud.com/37674
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Shaun Tancheff <shaun.tancheff@hpe.com>
Reviewed-by: Serguei Smirnov <ssmirnov@whamcloud.com>
Reviewed-by: Stephen Champion <stephen.champion@hpe.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/39575
Reviewed-by: Chris Horn <chris.horn@hpe.com>