[VOL-936] add changes to get distance between onu and olt

Change-Id: I3b5ab3d35baba2971fc8bbd895e8017e9719eb13
diff --git a/pkg/adapters/iAdapter.go b/pkg/adapters/iAdapter.go
index 112fb94..9436963 100644
--- a/pkg/adapters/iAdapter.go
+++ b/pkg/adapters/iAdapter.go
@@ -53,4 +53,5 @@
 	Disable_port(deviceId string, port *voltha.Port) error
 	Child_device_lost(parentDeviceId string, parentPortNo uint32, onuID uint32) error
 	Start_omci_test(device *voltha.Device, request *voltha.OmciTestRequest) (*voltha.TestResponse, error)
+	Get_ext_value(deviceId string, device *voltha.Device, valueflag voltha.ValueType_Type) (*voltha.ReturnValues, error)
 }