can: c_can: rename IF_RX -> IF_NAPI

can: c_can: rename IF_RX -> IF_NAPI

The C_CAN/D_CAN cores implement 2 interfaces to manage the message
objects. To avoid concurrency and the need for locking one interface
is used in the TX path (IF_TX). While the other one, named IF_RX is
used from NAPI context only. As this interface is not only used to
manage RX, but also TX message objects, this patch renames IF_RX to
IF_NAPI.

Link: https://lore.kernel.org/r/20210809080608.171545-1-mkl@pengutronix.de
Cc: Dario Binacchi <dariobin@libero.it>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>