LU-12424 lnet: prevent loop in LNetPrimaryNID()

LU-12424 lnet: prevent loop in LNetPrimaryNID()

If discovery is disabled locally or at the remote end, then attempt
discovery only once. Do not update the internal database when
discovery is disabled and do not repeat discovery.

This change prevents LNet from getting hung waiting for
discovery to complete.

Signed-off-by: Amir Shehata <ashehata@whamcloud.com>
Change-Id: I4543b0f71e6cf297a1a5f058ebcc6bf74b8ac328
Reviewed-on: https://review.whamcloud.com/35191
Reviewed-by: Olaf Weber <olaf.weber@hpe.com>
Tested-by: Jenkins
Reviewed-by: Chris Horn <hornc@cray.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>