autostart scripts: Reintroduce SYS_PARAM_VER (#22813)

The case where the airframe maintainer wants to enforce a reset to airframe is
not covered anymore with the `param set-default` mechanism. For products based
on PX4 this is still required to ensure proper functionality after a major update.

src/lib/systemlib/system_params.c

@@ -83,6 +83,19 @@ PARAM_DEFINE_INT32(SYS_AUTOCONFIG, 0);
  */
 PARAM_DEFINE_INT32(SYS_HITL, 0);
 
+/**
+ * Parameter version
+ *
+ * This is used internally only: an airframe configuration might set an expected
+ * parameter version value via PARAM_DEFAULTS_VER. This is checked on bootup
+ * against SYS_PARAM_VER, and if they do not match, parameters are reset and
+ * reloaded from the airframe configuration.
+ *
+ * @min 0
+ * @group System
+ */
+PARAM_DEFINE_INT32(SYS_PARAM_VER, 1);
+
 /**
  * Enable auto start of rate gyro thermal calibration at the next power up.
  *

src/modules/mavlink/mavlink_parameters.cpp

@@ -310,6 +310,9 @@ MavlinkParametersManager::send()
 		param_find("TRIG_MODE");
 		param_find("UAVCAN_ENABLE");
 
+		// parameter only used in startup script but should show on ground station
+		param_find("SYS_PARAM_VER");
+
 		_first_send = true;
 	}