Allow users to choose to whether send a BAM message or RTS/CTS #96
Description
Currently, j1939_21.py is written in a way that if PF is between 240 and 255, then TP messages are always sent as BAM; otherwise, it's RTS/CTS. However, I have run into times when I need to send BAM messages to a battery with addresses between 240 and 255. We can leave this choosing between BAM and RTS\CTS automatically as the default, but it should also give users an option to select whether it's BAM or RTS\CTS.