can: isotp: isotp_setsockopt(): only allow to set low level TX flags for CAN-FD

CAN-FD frames have struct canfd_frame::flags, while classic CAN frames
don't.

This patch refuses to set TX flags (struct
can_isotp_ll_options::tx_flags) on non CAN-FD isotp sockets.

Fixes: e057dd3fc2 ("can: add ISO 15765-2:2016 transport protocol")
Link: https://lore.kernel.org/r/20210218215434.1708249-2-mkl@pengutronix.de
Cc: Oliver Hartkopp <socketcan@hartkopp.net>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/isotp.c

@@ -1228,7 +1228,8 @@ static int isotp_setsockopt(struct socket *sock, int level, int optname,
 			if (ll.mtu != CAN_MTU && ll.mtu != CANFD_MTU)
 				return -EINVAL;
 
-			if (ll.mtu == CAN_MTU && ll.tx_dl > CAN_MAX_DLEN)
+			if (ll.mtu == CAN_MTU &&
+			    (ll.tx_dl > CAN_MAX_DLEN || ll.tx_flags != 0))
 				return -EINVAL;
 
 			memcpy(&so->ll, &ll, sizeof(ll));