Support receiving both standard and extended frames

[jxltom]

The RXM[1:0] bits (RXBnCTRL[6:5]) set special
Receive modes. Normally, these bits are cleared to ‘00’
to enable reception of all valid messages as determined by the appropriate acceptance filters. In this case, the determination of whether or not to receive
standard or extended messages is determined by the
EXIDE bit (RFXnSIDL[3]) in the Filter n Standard Identifier Low register.

As filters/masks are enabled in reset, then filtering of sid and eid are controlled by EXIDE of RXFnSIDL, as explained in datasheet 4.2.2. By default EXIDE is 0, so extended frames can not be received.

This PR makes MCP2515 able to receive sid and eid at the same time. Specifically, RXF0 is used for RXB0 and RXF1 is used for RXB1. The RXF0 can receive all standard frames and RXF1 can receive all extended frames.

Fixes #13, #23