LU-9971 lnet: fix peer ref counting

LU-9971 lnet: fix peer ref counting

Exit from the loop after peer ref count has been incremented
to avoid wrong ref count.

The code makes sure that a peer is queued for discovery at most
once if discovery is disabled. This is done to use discovery
as a standard ping for gateways which do not have discovery feature
or discovery is disabled.

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: I2cc4c8f9d780f5c438d9b51bb2d1106fec553f39
Reviewed-on: https://review.whamcloud.com/35446
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Reviewed-by: Chris Horn <hornc@cray.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>