Supporting Tx/Rx message direction for each interface

Pull request #773 adds is_rx attribute to can.Message. Currently this attribute is set to True by default. Functionality needs to be added to each interface type to set this attribute appropriately when building CAN messages:

- [x] ics_neovi (#773)
- [ ] ixxat
- [ ] kvaser
- [ ] pcan
- [ ] seedstudio
- [ ] serial
- [x] socketcan (#780)
- [ ] systec
- [ ] usb2can
- [x] vector (#852)
- [ ] nican
- [ ] iscan
- [x] virtual (#779)
- [ ] slcan
- [ ] robotell
- [ ] canalystii
- [x] CANtact (#853)

Start by reviewing how each unchecked interface builds can.Message, using the completed ics_neovi, socketcan, vector, virtual, and CANtact work as reference. Implement appropriate is_rx handling for the remaining interface types listed in the issue, and confirm each unchecked item behaves correctly when messages are received.

Scritto dal modello di indicizzazione a partire dal testo della issue.