[fix] bungee_takeoff was not turning motor on

Two issues:
- launch variable was not set to true which prevents the control to set
  throttle commad
- the autopilot_set_kill_throttle had not effects on fixedwing (in fact
  allows setting to true). We probably missed this because this function
  is mostly called to kill but not to resurect motor...

sw/airborne/firmwares/fixedwing/autopilot_generated.c

@@ -82,9 +82,10 @@ void autopilot_generated_set_mode(uint8_t new_autopilot_mode)
 }
 
 
-void autopilot_generated_set_motors_on(bool motors_on __attribute__((unused)))
+void autopilot_generated_set_motors_on(bool motors_on)
 {
-  // Do nothing on fixedwing ?
+  // only needed for consistency with other firmwares
+  autopilot.motors_on = motors_on;
 }
 
 static inline void copy_from_to_fbw(void)

sw/airborne/firmwares/fixedwing/autopilot_static.c

@@ -203,9 +203,12 @@ void autopilot_static_SetModeHandler(float new_autopilot_mode)
   autopilot_static_set_mode(new_autopilot_mode);
 }
 
-void autopilot_static_set_motors_on(bool motors_on __attribute__((unused)))
+void autopilot_static_set_motors_on(bool motors_on)
 {
-  // Do nothing on fixedwing ?
+  // it doesn't make real sense on fixedwing, as you can still use throttle
+  // in MAN and AUTO1 modes while have motor killed for AUTO2
+  // only needed for consistency with other firmwares
+  autopilot.motors_on = motors_on;
 }
 
 #ifdef FAILSAFE_DELAY_WITHOUT_GPS

sw/airborne/modules/nav/nav_bungee_takeoff.c

@@ -196,6 +196,7 @@ bool nav_bungee_takeoff_run(void)
       //Follow Launch Line
       NavVerticalAutoThrottleMode(BUNGEE_TAKEOFF_PITCH);
       NavVerticalThrottleMode(MAX_PPRZ * (BUNGEE_TAKEOFF_THROTTLE));
+      autopilot.launch = true; // turn on motor
       nav_route_xy(init_point.x, init_point.y, throttle_point.x, throttle_point.y);
       autopilot_set_kill_throttle(false);