usbnet: remove invalid check

skb->len is always non-negative.

The problem has been detected using proposed semantic patch
scripts/coccinelle/tests/unsigned_lesser_than_zero.cocci [1].

[1]: http://permalink.gmane.org/gmane.linux.kernel/2038576Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/usb/lan78xx.c

@@ -2424,11 +2424,6 @@ static int lan78xx_rx(struct lan78xx_net *dev, struct sk_buff *skb)
 			skb_pull(skb, align_count);
 	}
 
-	if (unlikely(skb->len < 0)) {
-		netdev_warn(dev->net, "invalid rx length<0 %d", skb->len);
-		return 0;
-	}
-
 	return 1;
 }
 

drivers/net/usb/smsc75xx.c

@@ -2185,11 +2185,6 @@ static int smsc75xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			skb_pull(skb, align_count);
 	}
 
-	if (unlikely(skb->len < 0)) {
-		netdev_warn(dev->net, "invalid rx length<0 %d\n", skb->len);
-		return 0;
-	}
-
 	return 1;
 }
 

drivers/net/usb/smsc95xx.c

@@ -1815,11 +1815,6 @@ static int smsc95xx_rx_fixup(struct usbnet *dev, struct sk_buff *skb)
 			skb_pull(skb, align_count);
 	}
 
-	if (unlikely(skb->len < 0)) {
-		netdev_warn(dev->net, "invalid rx length<0 %d\n", skb->len);
-		return 0;
-	}
-
 	return 1;
 }