can: make the number of echo skb's configurable

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, via:

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

The drivers have been adapted accordingly. Please check if the
value of echo_skb_max is OK for your driver.

Signed-off-by: Kurt Van Dijck <kurt.van.dijck@eia.be>
Signed-off-by: Wolfgang Grandegger <wg@grandegger.com>
git-svn-id: svn://svn.berlios.de//socketcan/trunk@1061 030b6a49-0b11-0410-94ab-b0dab22257f2