Error raised on invalid STmin value rather than using maximum default required in specification resulting in frame destruction

[davidflowers]

When a flow control frame is received with an invalid STmin value, the specification states that the longest STmin value shall be used (ISO 15765-2:2016 - 9.6.5.5).

This implementation will raise a value error resulting in the destruction of the frame rather than using the default maximum time:

python-can-isotp/isotp/protocol.py

Line 164 in 4a672ce

raise ValueError('Invalid StMin received in Flow Control')