create empty datalinkloss class for OBC

Currently the class does the same as the RTL class. It is now possible
 whichclass is sued in the navigator to handle datalink loss via a
 parameter

src/modules/navigator/navigator_params.c

@@ -37,6 +37,7 @@
  * Parameters for navigator in general
  *
  * @author Julian Oes <julian@oes.ch>
+ * @author Thomas Gubler <thomasgubler@gmail.com>
  */
 
 #include <nuttx/config.h>
@@ -64,3 +65,13 @@ PARAM_DEFINE_FLOAT(NAV_LOITER_RAD, 50.0f);
  * @group Mission
  */
 PARAM_DEFINE_FLOAT(NAV_ACC_RAD, 25.0f);
+
+/**
+ * Set OBC mode for data link loss
+ *
+ * If set to 1 the behaviour on data link loss is set to a mode according to the OBC rules
+ *
+ * @min 0
+ * @group Mission
+ */
+PARAM_DEFINE_INT32(NAV_DLL_OBC, 0);