neutron-lib: use L3 constant from neutron-lib

Ensure that the plugin uses the constant defined in neutron-lib.
L3_ROUTER_NAT will be dropped in favor of this. This change is in
https://review.openstack.org/#/c/394164/.

NeutronLibImpact
Partially-implements: blueprint neutron-lib

Change-Id: I6f569d8f914a92c27d97a2f82c8f693157222e16

networking_arista/l3Plugin/l3_arista.py

@@ -30,7 +30,6 @@ from neutron.db import db_base_plugin_v2
 from neutron.db import extraroute_db
 from neutron.db import l3_agentschedulers_db
 from neutron.db import l3_gwmode_db
-from neutron.plugins.common import constants
 from neutron.plugins.ml2.driver_context import NetworkContext  # noqa
 
 from networking_arista._i18n import _LE, _LI
@@ -75,7 +74,7 @@ class AristaL3ServicePlugin(db_base_plugin_v2.NeutronDbPluginV2,
         self.conn.consume_in_threads()
 
     def get_plugin_type(self):
-        return constants.L3_ROUTER_NAT
+        return n_const.L3
 
     def get_plugin_description(self):
         """Returns string description of the plugin."""