drivers: can: catch up on API naming changes

Catch up on the CAN driver API argument naming changes:
- Unify naming of callback function pointers as "callback".
- Unify naming of user-specified callback function arguments as
  "user_data".
- Instances and pointers to struct zcan_frame are named "frame",
  not "msg", to avoid confusion with the CAN message queue support.

Signed-off-by: Henrik Brix Andersen <hebad@vestas.com>