SITL: Add barometer drift parameter to the SITL library

libraries/SITL/SITL.cpp

@@ -47,6 +47,7 @@ const AP_Param::GroupInfo SITL::var_info[] PROGMEM = {
     AP_GROUPINFO("BATT_VOLTAGE",  19, SITL,  batt_voltage,  12.6),
     AP_GROUPINFO("ASPD_RND",      20, SITL,  aspd_noise,  0.5),
     AP_GROUPINFO("ACCEL_FAIL",    21, SITL,  accel_fail,  0),
+    AP_GROUPINFO("BARO_DRIFT",    22, SITL,  baro_drift,  0),
     AP_GROUPEND
 };
 

libraries/SITL/SITL.h

@@ -46,7 +46,8 @@ public:
 	static const struct AP_Param::GroupInfo var_info[];
 
 	// noise levels for simulated sensors
-	AP_Float baro_noise;  // in Pascals
+	AP_Float baro_noise;  // in metres
+	AP_Float baro_drift;  // in metres per second
 	AP_Float gyro_noise;  // in degrees/second
 	AP_Float accel_noise; // in m/s/s
 	AP_Float aspd_noise;  // in m/s