refactor(esp32-qemu-openeth): use lower half driver interface

[casaroli]

Summary

This current driver does not handle well netpkts used in the write buffers.

I learned about this document:

https://github.com/apache/nuttx/blob/master/Documentation/components/net/netdriver.rst

After I ported and contributed the original driver.

However from the document, I understand these types of drivers are simpler to implement and I could simplify the driver and handle correctly the TCP write buffers.

Impact

ESP32-opencores mac can handle writebuffers correctly.

Testing

Only local testing. Now I can even run mbedtls' ssl_client2.