Just ported the one Espressif distributes with ESP-IDF for ESP32, to ESP8266_RTOS_SDK v3.3:
https://github.com/DurvalMenezes/esp8266-iperf
As the original, this one works on both client *and* server modes (albeit I just tested the server mode).
Hope this can save someone some time instead of spending it porting the original like I did.
Cheers,
--
Durval.