RXB bit settings disagree with MCP2515 datasheet

[zbrown23]

In an (old) update datasheet for the MCP2515, Microchip states that setting the RXB[1:0] bits to a value other than '00' or '11' is not recommended. It seems as though Microchip doesn't recommend using the MCP2515's ability to specify filtering per standard vs extended frame formats.

arduino-mcp2515/mcp2515.h

Lines 289 to 290 in d424134

	static const uint8_t RXBnCTRL_RXM_STD = 0x20;
	static const uint8_t RXBnCTRL_RXM_EXT = 0x40;