[VOL-936] Add changes for onu distance from olt

Change-Id: I2d935194371d348e40a9926bb3a916b4893f48df
diff --git a/internal/pkg/core/openolt.go b/internal/pkg/core/openolt.go
index 6e35a3e..7343c94 100644
--- a/internal/pkg/core/openolt.go
+++ b/internal/pkg/core/openolt.go
@@ -389,3 +389,17 @@
 func (oo *OpenOLT) Start_omci_test(device *voltha.Device, request *voltha.OmciTestRequest) (*voltha.TestResponse, error) {
 	return nil, olterrors.ErrNotImplemented
 }
+
+func (oo *OpenOLT) Get_ext_value(deviceID string, device *voltha.Device, valueparam voltha.ValueType_Type) (*voltha.ReturnValues, error) {
+	var err error
+	resp := new(voltha.ReturnValues)
+	log.Infow("Get_ext_value", log.Fields{"device-id": deviceID, "onu-id": device.Id})
+	if handler := oo.getDeviceHandler(deviceID); handler != nil {
+		if resp, err = handler.getExtValue(device, valueparam); err != nil {
+			log.Errorw("error-occurred-during-get-ext-value", log.Fields{"device-id": deviceID, "onu-id": device.Id,
+				"error": err})
+			return nil, err
+		}
+	}
+	return resp, nil
+}