Extract chip specific code out of lasi_82596.c

Changes to last version:
- use netdev_alloc_skb
- make init_rx_bufs just fail and not panic, if skb alloc fails
- don/t free_irq, if request_irq failed

Thomas.

Extracted chip specific code out of lasi_82596.c and placed into a lib82596.c
to make it usable for other 82596 drivers
Signed-off-by: NThomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: NJeff Garzik <jeff@garzik.org>