Could you solve your problem in the meantime? I was in the same situation and found this thread when searching for advice. I found out that esp_wifi_internal_tx works, but esp_wifi_internal_reg_rxcb has no effect (IDF version 4.3). Finally I found a solution that works for me, and described it here:...

It may be late for you, but I also tried to run eth2wifi, failed first, and finally was successful. I had to make same changes to the ESP-IDF code to get it running on version 4.3. Here I wrote down details: https://github.com/makischu/ESP_eth2wifi Hope this is helpful for people in the same situati...

It might be late for you, but I had a similar problem, found this thread when searching for a solution, and finally found a solution. I have described it here:
https://github.com/makischu/ESP_eth2wifi