Fix slcan command and make it usable with slcand and ip commands.

[ondrasy]

Changes:

• The slCAN command FilterMask was not setting the mask.
• The open(), close() and listen_only() methods that had todo!() have been implemented. It now works with slcand and ip in Linux.

[GastonAznarez]

Hi, thanks for the contribution!

Have you tested this? If the answer is 'yes', could you provide more information on how you did it?

I will be testing this, stay tuned for updates.