Display neutron plugin options in globals.yml

Change-Id: I86244e68fac162b70f68356175e4550bd508b85c
Partially-Implements: blueprint update-configs

etc/kolla/globals.yml

@@ -67,6 +67,9 @@ network_interface: "eth0"
 # addresses for that reason.
 neutron_external_interface: "eth1"
 
+# Valid options are [ openvswitch, linuxbridge ]
+#neutron_plugin_agent: "openvswitch"
+
 
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 # OpenStack options