navigator: check distances between waypoints

Instead of just checking whether the first waypoint is too far away from
home it makes sense to also check between waypoints.
This can prevent
- flyaways due to user errors, or
- catch the corner case where a takeoff waypoint is added to a mission
  and therefore the first waypoint is not too far away, however, the
  subsequent waypoints are still too far away.

src/modules/navigator/mission_params.c

@@ -99,6 +99,22 @@ PARAM_DEFINE_INT32(MIS_ONBOARD_EN, 1);
  */
 PARAM_DEFINE_FLOAT(MIS_DIST_1WP, 900);
 
+/**
+ * Maximal horizontal distance between waypoint
+ *
+ * Failsafe check to prevent running missions which are way too big.
+ * Set a value of zero or less to disable. The mission will not be started if any distance between
+ * two subsequent waypoints is greater than MIS_DIST_WPS.
+ *
+ * @unit m
+ * @min 0
+ * @max 10000
+ * @decimal 1
+ * @increment 100
+ * @group Mission
+ */
+PARAM_DEFINE_FLOAT(MIS_DIST_WPS, 900);
+
 /**
  * Altitude setpoint mode
  *