Commander: add max flight time RTL

Adds COM_FLT_TIME_MAX param and logic in Commander to enforce RTL when
flight time is above this value. User can only override to LAND mode,
but not proceed flight beyond that.

Signed-off-by: Silvan Fuhrer <silvan@auterion.com>

src/modules/commander/commander_params.c

@@ -1065,3 +1065,21 @@ PARAM_DEFINE_INT32(COM_ARM_SDCARD, 1);
  * @unit m/s
  */
 PARAM_DEFINE_FLOAT(COM_WIND_WARN, -1.f);
+
+/**
+ * Maximum allowed flight time
+ *
+ * The vehicle aborts the current operation and returns to launch when
+ * the time since takeoff is above this value. It is not possible to resume the
+ * mission or switch to any mode other than RTL or Land.
+ *
+ * Set a nagative value to disable.
+ *
+ *
+ * @unit s
+ * @min -1
+ * @max 10000
+ * @value 0 Disable
+ * @group Commander
+ */
+PARAM_DEFINE_INT32(COM_FLT_TIME_MAX, -1);