Rover: change motor_active to be based on servo out rather than radio in

APMrover2/control_modes.cpp

@@ -119,7 +119,7 @@ bool Rover::motor_active()
 {
     // Check if armed and throttle is not neutral
     if (hal.util->get_soft_armed()) {
-        if (!channel_throttle->in_trim_dz()) {
+        if (channel_throttle->get_servo_out() != channel_throttle->get_radio_trim()) {
             return true;
         }
     }