Explicitly shutdown the socket connection in Udp/TcpTransport

This prevents 'Connection reset' errors on the Logstash side.

Author: eht16

logstash_async/transport.py

@@ -128,6 +128,7 @@ def _close(self, force=False):
             if self._sock:
                 while not self._is_sock_write_buff_empty():
                     time.sleep(0.05)
+                self._sock.shutdown(socket.SHUT_WR)
                 self._sock.close()
                 self._sock = None