drivers: can: shell: optionally bypass the shell when printing CAN frames

Optionally bypass the shell when printing received CAN frames in order not
to break up the line containing the frame. This allows for parsing the
printed CAN frames using Twisters pytest and console harnesses with the
cost of the shell ignoring input while the frame is being printed.

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