tc35815: 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: N"Eric W. Biederman" <ebiederm@xmission.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/ethernet/toshiba/tc35815.c

@@ -1645,6 +1645,9 @@ static int tc35815_poll(struct napi_struct *napi, int budget)
 	int received = 0, handled;
 	u32 status;
 
+	if (budget <= 0)
+		return received;
+
 	spin_lock(&lp->rx_lock);
 	status = tc_readl(&tr->Int_Src);
 	do {