Neutron: support BGP VPN service

Add ability to enable BGP VPN service and configure driver for it.
Corresponding model change: https://gerrit.mcp.mirantis.net/#/c/15779

Change-Id: I362d12efa49ef8c8b5b6d0352dc11863e0f63311
Related-Prod: PROD-17612
diff --git a/neutron/control/openvswitch/cluster.yml b/neutron/control/openvswitch/cluster.yml
index 80489c8..ca2e066 100644
--- a/neutron/control/openvswitch/cluster.yml
+++ b/neutron/control/openvswitch/cluster.yml
@@ -12,6 +12,8 @@
     neutron_tenant_network_types: "flat,vxlan"
     neutron_enable_qos: False
     neutron_enable_vlan_aware_vms: False
+    neutron_enable_bgp_vpn: False
+    neutron_bgp_vpn_driver: bagpipe
   neutron:
     server:
       global_physnet_mtu: ${_param:neutron_global_physnet_mtu}
@@ -19,6 +21,9 @@
       dvr: ${_param:neutron_control_dvr}
       qos: ${_param:neutron_enable_qos}
       vlan_aware_vms: ${_param:neutron_enable_vlan_aware_vms}
+      bgp_vpn:
+        enabled: ${_param:neutron_enable_bgp_vpn}
+        driver: ${_param:neutron_bgp_vpn_driver}
       backend:
         engine: ml2
         tenant_network_types: "${_param:neutron_tenant_network_types}"