Hi,
While converting a python2 script to python3 I noticed a bug in your library:

Traceback (most recent call last):
....
File "/opt/lib/scapy_http/http.py", line 179, in self_build
return _self_build(self, field_pos_list)
File "/opt/lib/scapy_http/http.py", line 101, in _self_build
val = _get_field_value(obj, f.name)
File "/opt/lib/scapy_http/http.py", line 74, in _get_field_value
headers = _parse_headers(val)
File "/opt/lib/scapy_http/http.py", line 18, in _parse_headers
headers = s.split("\r\n")
TypeError: a bytes-like object is required, not 'str'

I will open a PR which addresses this.