AP_ADSB: correct copying of callsign in Sagetech XP ADSB driver

this appeared to be overwriting all of the data at the start of the mavlink packet, rather than overwriting the callsign within the packet.

Author: peterbarker

libraries/AP_ADSB/AP_ADSB_Sagetech.cpp

@@ -241,7 +241,7 @@ void AP_ADSB_Sagetech::handle_adsb_in_msg(const Packet_XP &msg)
 
         if (msg.payload[16] != 0) {
             // if string is non-null, consider it valid
-            memcpy(&vehicle.info, &msg.payload[16], 8);
+            memcpy(&vehicle.info.callsign, &msg.payload[16], ARRAY_SIZE(vehicle.info.callsign)-1);  // "The callsign, 8+null" means we subtract one here
             vehicle.info.flags |= ADSB_FLAGS_VALID_CALLSIGN;
         }