Plane: integrate parachute check_sink_rate

this was previously part of the update function.  It can be run before or after the update

ArduPlane/parachute.cpp

@@ -8,6 +8,7 @@ void Plane::parachute_check()
 {
 #if PARACHUTE == ENABLED
     parachute.update();
+    parachute.check_sink_rate();
 #endif
 }