can: can327: flush TX_work on ldisc .close()

can: can327: flush TX_work on ldisc .close()

Additionally, remove it from .ndo_stop().

This ensures that the worker is not called after being freed, and that
the UART TX queue remains active to send final commands when the
netdev is stopped.

Thanks to Jiri Slaby for finding this in slcan:

  https://lore.kernel.org/linux-can/20221201073426.17328-1-jirislaby@kernel.org/

A variant of this patch for slcan, with the flush in .ndo_stop() still
present, has been tested successfully on physical hardware:

  https://bugzilla.suse.com/show_bug.cgi?id=1205597

Fixes: 43da2f07622f ("can: can327: CAN/ldisc driver for ELM327 based OBD-II adapters")
Cc: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: Max Staudt <max@enpas.org>
Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: Marc Kleine-Budde <mkl@pengutronix.de>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: linux-can@vger.kernel.org
Cc: netdev@vger.kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: Max Staudt <max@enpas.org>
Link: https://lore.kernel.org/all/20221202160148.282564-1-max@enpas.org
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>