Tracker: move init of DataFlash references into vehicle init

This makes it look like the other vehicle types

AntennaTracker/Log.cpp

@@ -90,7 +90,6 @@ void Tracker::start_logging()
     if (g.log_bitmask != 0) {
         if (!logging_started) {
             logging_started = true;
-            DataFlash.setVehicle_Startup_Log_Writer(FUNCTOR_BIND(&tracker, &Tracker::Log_Write_Vehicle_Startup_Messages, void));
             DataFlash.StartNewLog();
         }
         // enable writes

AntennaTracker/system.cpp

@@ -86,6 +86,9 @@ void Tracker::init_tracker()
 
     init_barometer(true);
 
+    // initialise DataFlash library
+    DataFlash.setVehicle_Startup_Log_Writer(FUNCTOR_BIND(&tracker, &Tracker::Log_Write_Vehicle_Startup_Messages, void));
+
     // set serial ports non-blocking
     serial_manager.set_blocking_writes_all(false);