Rover: move motors_active to be motors.active

This will help when we come to subclass the Motors library.

APMrover2/APMrover2.cpp

@@ -105,7 +105,7 @@ constexpr int8_t Rover::_failsafe_priorities[7];
 */
 void Rover::stats_update(void)
 {
-    g2.stats.set_flying(motor_active());
+    g2.stats.set_flying(g2.motors.active());
     g2.stats.update();
 }
 #endif

APMrover2/AP_MotorsUGV.cpp

@@ -673,3 +673,24 @@ float AP_MotorsUGV::get_scaled_throttle(float throttle) const
     const float throttle_pct = constrain_float(throttle, -100.0f, 100.0f) / 100.0f;
     return 100.0f * sign * ((_thrust_curve_expo - 1.0f) + safe_sqrt((1.0f - _thrust_curve_expo) * (1.0f - _thrust_curve_expo) + 4.0f * _thrust_curve_expo * fabsf(throttle_pct))) / (2.0f * _thrust_curve_expo);
 }
+
+// return true if motors are moving
+bool AP_MotorsUGV::active() const
+{
+    // if soft disarmed, motors not active
+    if (!hal.util->get_soft_armed()) {
+        return false;
+    }
+
+    // check throttle is active
+    if (!is_zero(get_throttle())) {
+        return true;
+    }
+
+    // skid-steering vehicles active when steering
+    if (have_skid_steering() && !is_zero(get_steering())) {
+        return true;
+    }
+
+    return false;
+}

APMrover2/AP_MotorsUGV.h

@@ -28,6 +28,9 @@ public:
     // initialise motors
     void init();
 
+    // return true if motors are active
+    bool active() const;
+
     // setup output in case of main CPU failure
     void setup_safety_output();
 

APMrover2/Rover.h

@@ -443,7 +443,6 @@ private:
     void do_aux_function_change_mode(Mode &mode,
                                      const aux_switch_pos ch_flag);
     void read_aux_switch();
-    bool motor_active();
 
     // crash_check.cpp
     void crash_check();

APMrover2/control_modes.cpp

@@ -265,24 +265,3 @@ void Rover::read_aux_switch()
         break;
     }
 }
-
-// return true if motors are moving
-bool Rover::motor_active()
-{
-    // if soft disarmed, motors not active
-    if (!hal.util->get_soft_armed()) {
-        return false;
-    }
-
-    // check throttle is active
-    if (!is_zero(g2.motors.get_throttle())) {
-        return true;
-    }
-
-    // skid-steering vehicles active when steering
-    if (g2.motors.have_skid_steering() && !is_zero(g2.motors.get_steering())) {
-        return true;
-    }
-
-    return false;
-}

APMrover2/radio.cpp

@@ -80,7 +80,7 @@ void Rover::rudder_arm_disarm_check()
             // not at full right rudder
             rudder_arm_timer = 0;
         }
-    } else if (!motor_active()) {
+    } else if (!g2.motors.active()) {
         // when armed and motor not active (not moving), full left rudder starts disarming counter
         if (channel_steer->get_control_in() < -4000) {
             const uint32_t now = millis();