Copter: land mode inits auto yaw

ArduCopter/mode_land.cpp

@@ -34,6 +34,9 @@ bool ModeLand::init(bool ignore_checks)
     // reset flag indicating if pilot has applied roll or pitch inputs during landing
     copter.ap.land_repo_active = false;
 
+    // initialise yaw
+    auto_yaw.set_mode(AUTO_YAW_HOLD);
+
     return true;
 }