Copter: set_range on motor interlock channel

ArduCopter/heli.cpp

@@ -132,6 +132,7 @@ float Copter::get_pilot_desired_rotor_speed() const
 {
     RC_Channel *rc_ptr = rc().find_channel_for_option(RC_Channel::AUX_FUNC::MOTOR_INTERLOCK);
     if (rc_ptr != nullptr) {
+        rc_ptr->set_range(1000);
         return (float)rc_ptr->get_control_in() * 0.001f;
     }
     return 0.0f;