[IFB]: Fix crash on input device removal

The input_device pointer is not refcounted, which means the device may
disappear while packets are queued, causing a crash when ifb passes packets
with a stale skb->dev pointer to netif_rx().

Fix by storing the interface index instead and do a lookup where neccessary.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Acked-by: Jamal Hadi Salim <hadi@cyberus.ca>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/pkt_cls.h b/include/net/pkt_cls.h
index b902d24..02647fe 100644
--- a/include/net/pkt_cls.h
+++ b/include/net/pkt_cls.h
@@ -352,10 +352,13 @@
 static inline int
 tcf_match_indev(struct sk_buff *skb, char *indev)
 {
+	struct net_device *dev;
+
 	if (indev[0]) {
-		if  (!skb->input_dev)
+		if  (!skb->iif)
 			return 0;
-		if (strcmp(indev, skb->input_dev->name))
+		dev = __dev_get_by_index(skb->iif);
+		if (!dev || strcmp(indev, dev->name))
 			return 0;
 	}