Option neutron_plugin_agent: "opendaylight" added

Added the missing option neutron_plugin_agent: "opendaylight" added to
the opendaylight documentation page. Without it the deployment would
not use the neutron_plugin_agent but the default one: openvswitch .

Change-Id: I56a377e1faab9a50f36383ea59b45bf5a9155bcf

doc/source/reference/networking/opendaylight.rst

@@ -12,6 +12,7 @@ Modify the ``/etc/kolla/globals.yml`` file as the following example shows:
 .. code-block:: yaml
 
    enable_opendaylight: "yes"
+   neutron_plugin_agent: "opendaylight"
 
 Networking-ODL is an additional Neutron plugin that allows the OpenDaylight
 SDN Controller to utilize its networking virtualization features.