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.
b8c1ce45e6