update mqttd main.c, fix debug with java bug for JSON with \0 bug

guowenxue

2019-08-03 1ba740d4f23b97f105bbc3dd9780904f422a766c

 apue/2.Socket/socket_client.c

@@ -109,7 +109,8 @@
          }
       }

       //printf("Read %d bytes data from server: '%s'\n", rv, buf);

       sleep(5);
    }