LU-12411 lnet: Do not allow gateways on remote nets

LU-12411 lnet: Do not allow gateways on remote nets

A gateway needs to be reachable over some local interface.

Lustre-change: https://review.whamcloud.com/35198
Lustre-commit: 43b35351e9ca258773e89c2d68047e939fb822fb

Signed-off-by: Chris Horn <hornc@cray.com>
Change-Id: Ib66d4f8fd48d8863097280c480648ab8e29d2767
Reviewed-by: Amir Shehata <ashehata@whamcloud.com>
Reviewed-by: Sonia Sharma <sharmaso@whamcloud.com>
Signed-off-by: Minh Diep <mdiep@whamcloud.com>
Reviewed-on: https://review.whamcloud.com/36870
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Oleg Drokin <green@whamcloud.com>