LU-9913 lnet: balance references in lnet_discover_peer_locked()

LU-9913 lnet: balance references in lnet_discover_peer_locked()

In lnet_discover_peer_locked() avoid a leaked reference to the peer in
the non-blocking discovery case.

Signed-off-by: John L. Hammond <john.hammond@intel.com>
Change-Id: Ic48414859c923af1ebb197b0b0f2f8d6752043ac
Reviewed-on: https://review.whamcloud.com/28695
Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Quentin Bouget <quentin.bouget@cea.fr>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>