can: make the number of echo skb's configurable

This patch allows the CAN controller driver to define the number of echo
skb's used for the local loopback (echo), as suggested by Kurt Van
Dijck, with the function:

  struct net_device *alloc_candev(int sizeof_priv,
                                  unsigned int echo_skb_max);

The CAN drivers have been adapted accordingly. For the ems_usb driver,
as suggested by Sebastian Haas, the number of echo skb's has been
increased to 10, which improves the transmission performance a lot.

Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
Signed-off-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
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 814e6c5..23a7128 100644
--- a/drivers/net/can/ti_hecc.c
+++ b/drivers/net/can/ti_hecc.c
@@ -74,10 +74,6 @@
 #define HECC_MB_TX_SHIFT	2 /* as per table above */
 #define HECC_MAX_TX_MBOX	BIT(HECC_MB_TX_SHIFT)
 
-#if (HECC_MAX_TX_MBOX > CAN_ECHO_SKB_MAX)
-#error "HECC: MAX TX mailboxes should be equal or less than CAN_ECHO_SKB_MAX"
-#endif
-
 #define HECC_TX_PRIO_SHIFT	(HECC_MB_TX_SHIFT)
 #define HECC_TX_PRIO_MASK	(MAX_TX_PRIO << HECC_MB_TX_SHIFT)
 #define HECC_TX_MB_MASK		(HECC_MAX_TX_MBOX - 1)
@@ -902,7 +898,7 @@
 		goto probe_exit_free_region;
 	}
 
-	ndev = alloc_candev(sizeof(struct ti_hecc_priv));
+	ndev = alloc_candev(sizeof(struct ti_hecc_priv), HECC_MAX_TX_MBOX);
 	if (!ndev) {
 		dev_err(&pdev->dev, "alloc_candev failed\n");
 		err = -ENOMEM;