LU-10453 lnet: support gni net configuration

GNI interfaces don't have IP addresses so when configuring GNI
interfaces there is no point of trying to query the ip. There is
also only one GNI interface, therefore the net configuration
command shouldn't enforce an interface name.

This patch also adds more descriptive error commands. It also allows
deleting an entire network without having to specify an interface.

Test-Parameters: trivial
Signed-off-by: Amir Shehata <amir.shehata@intel.com>
Change-Id: I549647675fe5530db7d86272a7dc79892117847d
Reviewed-on: https://review.whamcloud.com/30829


Tested-by: Jenkins
Tested-by: Maloo <hpdd-maloo@intel.com>
Reviewed-by: Dmitry Eremin <dmitry.eremin@intel.com>
Reviewed-by: James Simmons <uja.ornl@yahoo.com>
Reviewed-by: Oleg Drokin <oleg.drokin@intel.com>