Centralized executor

core/src/mindustry/net/ArcNetProvider.java

@@ -24,7 +24,6 @@ import static mindustry.Vars.*;
 public class ArcNetProvider implements NetProvider{
     final Client client;
     final Prov<DatagramPacket> packetSupplier = () -> new DatagramPacket(new byte[512], 512);
-    final ExecutorService executor = Threads.executor(1);
 
     final Server server;
     final CopyOnWriteArrayList<ArcConnection> connections = new CopyOnWriteArrayList<>();
@@ -263,7 +262,7 @@ public class ArcNetProvider implements NetProvider{
     @Override
     public void closeServer(){
         connections.clear();
-        executor.submit(server::stop);
+        mainExecutor.submit(server::stop);
     }
 
     ArcConnection getByArcID(int id){