Fix L3 plugin to match with upstream
Fix L3 plugin to match with upstream

An upstream code was changed to get the tenant_id for router.
This patch fixes L3 plugin to match with the upstream fix

Change-Id: I20ba82d014cbe8fabae59cfeded53dd1f8af88f2

openstack/networking-arista,openstack/networking-arista,stackforge/networking-arista