Fixing L3 Plugin to match with upstream change
Fixing L3 Plugin to match with upstream change

A fix was pushed in neutron upstream which broke this plugin.
This patch fixes this.

Change-Id: I286e96db2b58a92e69edeb1b85bb1e3f9cf22e6f

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