can: j1939: j1939_send_one(): fix missing CAN header initialization

The read access to struct canxl_frame::len inside of a j1939 created
skbuff revealed a missing initialization of reserved and later filled
elements in struct can_frame.

This patch initializes the 8 byte CAN header with zero.

Fixes: 9d71dd0c ("can: add support of SAE J1939 protocol")
Cc: Oleksij Rempel <o.rempel@pengutronix.de>
Link: https://lore.kernel.org/linux-can/20221104052235.GA6474@pengutronix.de
Reported-by: syzbot+d168ec0caca4697e03b1@syzkaller.appspotmail.com
Signed-off-by: Oliver Hartkopp <socketcan@hartkopp.net>
Link: https://lore.kernel.org/all/20221104075000.105414-1-socketcan@hartkopp.net
Cc: stable@vger.kernel.org
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>

net/can/j1939/main.c

@@ -336,6 +336,9 @@ int j1939_send_one(struct j1939_priv *priv, struct sk_buff *skb)
 	/* re-claim the CAN_HDR from the SKB */
 	cf = skb_push(skb, J1939_CAN_HDR);
 
+	/* initialize header structure */
+	memset(cf, 0, J1939_CAN_HDR);
+
 	/* make it a full can frame again */
 	skb_put(skb, J1939_CAN_FTR + (8 - dlc));