Define a preferred port.

server/src/main/java/org/briarproject/interferometer/server/Server.java

@@ -15,6 +15,7 @@ import static java.util.logging.Logger.getLogger;
 
 public class Server {
 
+	private static final int PREFERRED_PORT = 40404;
 	private static final byte CONNECTION_TYPE_UPLOAD = 0;
 	private static final byte CONNECTION_TYPE_DOWNLOAD = 1;
 	private static final int BUFFER_SIZE = 4096;
@@ -28,7 +29,7 @@ public class Server {
 	}
 
 	private void run() throws IOException {
-		ServerSocket ss = new ServerSocket(0);
+		ServerSocket ss = new ServerSocket(PREFERRED_PORT);
 		LOG.info("Listening on port " + ss.getLocalPort());
 		//noinspection InfiniteLoopStatement
 		while (true) {