chelsio: more rx speedup

Cleanup receive processing some more:
   * do the reserve padding of skb during setup
   * don't pass constants to get_packet
   * do smart prefetch of skb
   * make copybreak a module parameter

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: Jeff Garzik <jeff@garzik.org>