Add support for remote CAN frames on LPC11CXX

* Fixed bug where outgoing messages always had `DIR` bit set, even if message type was `CANRemote`.
* Fixed TODO where incoming messages were always assigned message type `CANData` even if the message was remote
* Changed filter setup to no longer set `MDIR` bit in receive filter; this allows remote messages to pass through the filter.

I've tested this on an LPC11C14 and seems to work fine. The one caveat is that the filter no longer prevents remote messages from showing up in `CAN.read()` (though the message type is now set correctly). I'm not sure what the default behavior for filtering data vs remote frames on other platforms is right now.

Perhaps the filter API should include an enum for filtering message of type CANData vs CANRemote vs either.