netinfo: add gateway reporting to all devices

by adding gateway reporting to all the devices we make it possible
to for a vdsm client to gather which is the gateway of the device
that is to be used for providing link to a bridged (VM) network.

Change-Id: I5dc4730214efa9eaba8425c3bf4842441b97084f
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/28704
Reviewed-by: Dan Kenigsberg <danken@redhat.com>