This feature allows `httpd_req_recv()` and `httpd_send()` functions to return
specific `HTTPD_SOCK_ERR_` codes in case of socket errors. This is useful
in case of errors like `EAGAIN`, `EINTR`, etc. when the user may want to
retry `httpd_req_recv()` / `httpd_send()` function call.
Content-Length header should not be included when using chunked encoding.
Some browsers will close the socket after seeing the 0 sized response instead of
reading the chunks.
Merges https://github.com/espressif/esp-idf/pull/2458
