sky2: Shut off interrupts before NAPI

Interrupts should be masked, then synchronized, and
finally NAPI should be disabled.

Signed-off-by: Mike McCormack <mikem@ring3k.org>
Acked-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>