can: provide library functions for skb allocation

This patch makes the private functions alloc_can_skb() and
alloc_can_err_skb() of the at91_can driver public and adapts all
drivers to use these. While making the patch I realized, that
the skb's are *not* setup consistently. It's now done as shown
below:

  skb->protocol = htons(ETH_P_CAN);
  skb->pkt_type = PACKET_BROADCAST;
  skb->ip_summed = CHECKSUM_UNNECESSARY;
  *cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
  memset(*cf, 0, sizeof(struct can_frame));

The frame is zeroed out to avoid uninitialized data to be passed to
user space. Some drivers or library code did not set "pkt_type" or
"ip_summed". Also,  "__constant_htons()" should not be used for
runtime invocations, as pointed out by David Miller.

Signed-off-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 23a7128..07e8016 100644
--- a/drivers/net/can/ti_hecc.c
+++ b/drivers/net/can/ti_hecc.c
@@ -535,18 +535,15 @@
 	u32 data, mbx_mask;
 	unsigned long flags;
 
-	skb = netdev_alloc_skb(priv->ndev, sizeof(struct can_frame));
+	skb = alloc_can_skb(priv->ndev, &cf);
 	if (!skb) {
 		if (printk_ratelimit())
 			dev_err(priv->ndev->dev.parent,
-				"ti_hecc_rx_pkt: netdev_alloc_skb() failed\n");
+				"ti_hecc_rx_pkt: alloc_can_skb() failed\n");
 		return -ENOMEM;
 	}
-	skb->protocol = __constant_htons(ETH_P_CAN);
-	skb->ip_summed = CHECKSUM_UNNECESSARY;
 
 	mbx_mask = BIT(mbxno);
-	cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
 	data = hecc_read_mbx(priv, mbxno, HECC_CANMID);
 	if (data & HECC_CANMID_IDE)
 		cf->can_id = (data & CAN_EFF_MASK) | CAN_EFF_FLAG;
@@ -656,19 +653,13 @@
 	struct sk_buff *skb;
 
 	/* propogate the error condition to the can stack */
-	skb = netdev_alloc_skb(ndev, sizeof(struct can_frame));
+	skb = alloc_can_err_skb(ndev, &cf);
 	if (!skb) {
 		if (printk_ratelimit())
 			dev_err(priv->ndev->dev.parent,
-				"ti_hecc_error: netdev_alloc_skb() failed\n");
+				"ti_hecc_error: alloc_can_err_skb() failed\n");
 		return -ENOMEM;
 	}
-	skb->protocol = __constant_htons(ETH_P_CAN);
-	skb->ip_summed = CHECKSUM_UNNECESSARY;
-	cf = (struct can_frame *)skb_put(skb, sizeof(struct can_frame));
-	memset(cf, 0, sizeof(struct can_frame));
-	cf->can_id = CAN_ERR_FLAG;
-	cf->can_dlc = CAN_ERR_DLC;
 
 	if (int_status & HECC_CANGIF_WLIF) { /* warning level int */
 		if ((int_status & HECC_CANGIF_BOIF) == 0) {