Expand code for supporting multiple CAN ports

[xabirizar9]

Good morning,

I was just going through the code and unless I saw it wrong, the library doesn't seem to support multiple CAN ports. I have an attachment to the raspberry pi that has 2 CAN ports and would like to separate the messages across them, instead of sending them via the same port just with a different ID.

Just double checking because this seems like such an obvious thing to implement, and I'd happily submit a PR where I extend the code with this functionality.

Best,

Xabi