[io][asc]: parser / writer using DLC as data length #1245

Describe the bug

Reader
https://github.com/hardbyte/python-can/blob/develop/can/io/asc.py#L197: using DLC (data length code) from ASC as dlc (Data length) in python-can message. I think data_length must be used instead

Writer
https://github.com/hardbyte/python-can/blob/develop/can/io/asc.py#L384: inverse is done here. instead len2dlc(msg.dlc)

To Reproduce

asc_bug.py at python-can root

from pathlib import Path
from can import LogReader

if __name__ == "__main__":
    path = Path(__file__).parent / "test" / "data" / "test_CanFdMessage64.asc"
    reader = LogReader(path)
    for msg in reader:
        print(msg)

output:

Timestamp:       30.506898        ID: 04ee    S Rx     F    EI    DL: 15    a1 02 03 04 00 00 00 00 00 00 00 00 00 00 00    Channel: 3
Timestamp:       31.506898    ID: 1c4d80a7    X Rx     F BS       DL: 15    b1 02 03 04 00 00 00 00 00 00 00 00 00 00 00    Channel: 3

In the test_CanFdMessage64.asc frames are 64 bytes length

Expected behavior

frames should have 64 bytes length

Additional context

used python-can is develop branch