slip: fix NOHZ local_softirq_pending 08 warning

When using nanosleep() in an userspace application we get a ratelimit warning:

	NOHZ: local_softirq_pending 08

According to 481a8199 the problem is caused by
netif_rx() function. This patch replaces netif_rx() with netif_rx_ni() which
has to be used from process/softirq context.
Signed-off-by: NMatvejchikov Ilya <matvejchikov@gmail.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/slip.c

@@ -367,7 +367,7 @@ static void sl_bump(struct slip *sl)
 	memcpy(skb_put(skb, count), sl->rbuff, count);
 	skb_reset_mac_header(skb);
 	skb->protocol = htons(ETH_P_IP);
-	netif_rx(skb);
+	netif_rx_ni(skb);
 	dev->stats.rx_packets++;
 }