AP_Baro: change to a 7 point DerivativeFilter for climb rate

libraries/AP_Baro/AP_Baro.cpp

@@ -91,7 +91,7 @@ float AP_Baro::get_climb_rate(void)
 
     // we use a 9 point derivative filter on the climb rate. This seems
     // to produce somewhat reasonable results on real hardware
-    _climb_rate = _climb_rate_filter.apply(get_altitude());
+    _climb_rate = _climb_rate_filter.apply(get_altitude(), _last_update) * 1.0e3;
 
 	return _climb_rate;
 }

libraries/AP_Baro/AP_Baro.h

@@ -50,7 +50,7 @@ private:
     float       _climb_rate;
     uint32_t    _last_climb_rate_t;
     uint32_t    _last_altitude_t;
-    DerivativeFilter<float,float,9> _climb_rate_filter;
+    DerivativeFilterFloat_Size7 _climb_rate_filter;
 };
 
 #include "AP_Baro_MS5611.h"