net: use CHECKSUM_NONE instead of magic number

Two places in the kernel were doing skb->ip_summed = 0.

Change both to skb->ip_summed = CHECKSUM_NONE, which is more readable.

Signed-off-by: Cesar Eduardo Barros <cesarb@cesarb.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ksz884x.c b/drivers/net/ksz884x.c
index 540a8dc..7f7d570 100644
--- a/drivers/net/ksz884x.c
+++ b/drivers/net/ksz884x.c
@@ -4898,7 +4898,7 @@
 				goto unlock;
 			}
 			skb_copy_and_csum_dev(org_skb, skb->data);
-			org_skb->ip_summed = 0;
+			org_skb->ip_summed = CHECKSUM_NONE;
 			skb->len = org_skb->len;
 			copy_old_skb(org_skb, skb);
 		}