Use aux 5 to set preferred pitch for the rotating wing drone

sw/airborne/modules/radio_control/rc_datalink.h

@@ -44,6 +44,7 @@
 #define RADIO_AUX2      6
 #define RADIO_AUX4      7
 #define RADIO_AUX6      8
+#define RADIO_AUX5      9
 
 extern int8_t rc_dl_values[ RC_DL_NB_CHANNEL ];
 extern volatile bool rc_dl_frame_available;