sky2: Don't receive packets when the napi budget == 0

Processing any incoming packets with a with a napi budget of 0
is incorrect driver behavior.

This matters as netpoll will shortly call drivers with a budget of 0
to avoid receive packet processing happening in hard irq context.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ethernet/marvell/sky2.c b/drivers/net/ethernet/marvell/sky2.c
index 5a5b237..d524676 100644
--- a/drivers/net/ethernet/marvell/sky2.c
+++ b/drivers/net/ethernet/marvell/sky2.c
@@ -2735,6 +2735,9 @@
 	unsigned int total_bytes[2] = { 0 };
 	unsigned int total_packets[2] = { 0 };
 
+	if (to_do <= 0)
+		return work_done;
+
 	rmb();
 	do {
 		struct sky2_port *sky2;