Arranging name of gateway parameter

The patch changes gateway to gateway_ip parameter in reclass to be
set properly during subnet creation by neuton.client state.
https://github.com/salt-formulas/salt-formula-neutron/blob/master/neutron/client.sls#L94

Change-Id: Ic5c0249456e891bf519c49852d2c818626a23025
Related-PROD: PROD-19395
diff --git a/neutron/client/service/public.yml b/neutron/client/service/public.yml
index c3e2ca3..532a8cf 100644
--- a/neutron/client/service/public.yml
+++ b/neutron/client/service/public.yml
@@ -21,5 +21,5 @@
                   allocation_pools:
                     - start: ${_param:openstack_public_neutron_subnet_allocation_start}
                       end: ${_param:openstack_public_neutron_subnet_allocation_end}
-                  gateway: ${_param:openstack_public_neutron_subnet_gateway}
+                  gateway_ip: ${_param:openstack_public_neutron_subnet_gateway}
                   enable_dhcp: False