add fast open support in server

shadowsocks/tcprelay.py

@@ -400,6 +400,11 @@ class TCPRelay(object):
         server_socket.bind(sa)
         server_socket.setblocking(False)
         server_socket.listen(1024)
+        if config['fast_open']:
+            try:
+                server_socket.setsockopt(socket.SOL_TCP, 23, 5)
+            except socket.error:
+                logging.error('warning: fast open is not available')
         self._server_socket = server_socket
 
     def add_to_loop(self, loop):