only set no_delay on TCP sockets

otherwise and exception is thrown on when connecting to unix_socket
([Errno 95] Operation not supported).

pymysql/connections.py

@@ -839,10 +839,10 @@ class Connection(object):
                         raise
                 self.host_info = "socket %s:%d" % (self.host, self.port)
                 if DEBUG: print('connected using socket')
+                if self.no_delay:
+                    sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
             sock.settimeout(None)
             sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
-            if self.no_delay:
-                sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_NODELAY, 1)
             self.socket = sock
             self._rfile = _makefile(sock, 'rb')
             self._get_server_information()