[PATCH] sky2: status interrupt handling improvement

More changes to prevent losing status and causing hangs.
The hardware is smarter than I gave it credit for.
Clearing the status IRQ causes the status state machine to
toggle an IRQ if needed and post any more transmits.

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