Add OpenConfig based port statistics discovery

Change-Id: I3e7d5683f8a51d06db18b644963044d204911346
diff --git a/drivers/gnmi/src/main/resources/gnmi-drivers.xml b/drivers/gnmi/src/main/resources/gnmi-drivers.xml
index 70c0b20..9af162f 100644
--- a/drivers/gnmi/src/main/resources/gnmi-drivers.xml
+++ b/drivers/gnmi/src/main/resources/gnmi-drivers.xml
@@ -20,6 +20,8 @@
                    impl="org.onosproject.drivers.gnmi.OpenConfigGnmiDeviceDescriptionDiscovery"/>
         <behaviour api="org.onosproject.net.device.DeviceHandshaker"
                    impl="org.onosproject.drivers.gnmi.GnmiHandshaker"/>
+        <behaviour api="org.onosproject.net.device.PortStatisticsDiscovery"
+                   impl="org.onosproject.drivers.gnmi.OpenConfigGnmiPortStatisticsDiscovery"/>
     </driver>
 </drivers>