can: isotp: tx-path: zero initialize outgoing CAN frames

Commit d4eb538e ("can: isotp: TX-path: ensure that CAN frame flags are
initialized") ensured the TX flags to be properly set for outgoing CAN
frames.

In fact the root cause of the issue results from a missing initialization
of outgoing CAN frames created by isotp. This is no problem on the CAN bus
as the CAN driver only picks the correctly defined content from the struct
can(fd)_frame. But when the outgoing frames are monitored (e.g. with
candump) we potentially leak some bytes in the unused content of
struct can(fd)_frame.

Fixes: e057dd3f ("can: add ISO 15765-2:2016 transport protocol")
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Link: https://lore.kernel.org/r/20210319100619.10858-1-socketcan@hartkopp.net


Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>