MCP2515 `observe` sets configuration mode

[ghost]

There's a method called MCP2515::observe, which writes 100, which is however configuration mode (http://ww1.microchip.com/downloads/en/DeviceDoc/MCP2515-Stand-Alone-CAN-Controller-with-SPI-20001801J.pdf).

The method is not documented in API.md, however I'd think that it means to enable listen-only mode. Listen-only mode is however 011, which is 0x60.