can: Unify droping of invalid tx skbs and netdev stats

To prevent the CAN drivers to operate on invalid socketbuffers the skbs are
now checked and silently dropped at the xmit-function consistently.

Also the netdev stats are consistently using the CAN data length code (dlc)
for [rx|tx]_bytes now.

Signed-off-by: Oliver Hartkopp <oliver@hartkopp.net>
Acked-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/can/ti_hecc.c b/drivers/net/can/ti_hecc.c
index 5c993c2..7d370e3 100644
--- a/drivers/net/can/ti_hecc.c
+++ b/drivers/net/can/ti_hecc.c
@@ -477,6 +477,9 @@
 	u32 mbxno, mbx_mask, data;
 	unsigned long flags;
 
+	if (can_dropped_invalid_skb(ndev, skb))
+		return NETDEV_TX_OK;
+
 	mbxno = get_tx_head_mb(priv);
 	mbx_mask = BIT(mbxno);
 	spin_lock_irqsave(&priv->mbx_lock, flags);
@@ -491,7 +494,6 @@
 	spin_unlock_irqrestore(&priv->mbx_lock, flags);
 
 	/* Prepare mailbox for transmission */
-	data = min_t(u8, cf->can_dlc, 8);
 	if (cf->can_id & CAN_RTR_FLAG) /* Remote transmission request */
 		data |= HECC_CANMCF_RTR;
 	data |= get_tx_head_prio(priv) << 8;