[NET]: Treat CHECKSUM_PARTIAL as CHECKSUM_UNNECESSARY

When a transmitted packet is looped back directly, CHECKSUM_PARTIAL
maps to the semantics of CHECKSUM_UNNECESSARY.  Therefore we should
treat it as such in the stack.

Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/udp.c b/net/ipv4/udp.c
index 5ad7a26..cec0f2c 100644
--- a/net/ipv4/udp.c
+++ b/net/ipv4/udp.c
@@ -848,7 +848,7 @@
 			goto csum_copy_err;
 	}
 
-	if (skb->ip_summed == CHECKSUM_UNNECESSARY)
+	if (skb_csum_unnecessary(skb))
 		err = skb_copy_datagram_iovec(skb, sizeof(struct udphdr),
 					      msg->msg_iov, copied       );
 	else {
@@ -1190,7 +1190,7 @@
 				      proto, skb->csum))
 			skb->ip_summed = CHECKSUM_UNNECESSARY;
 	}
-	if (skb->ip_summed != CHECKSUM_UNNECESSARY)
+	if (!skb_csum_unnecessary(skb))
 		skb->csum = csum_tcpudp_nofold(iph->saddr, iph->daddr,
 					       skb->len, proto, 0);
 	/* Probably, we should checksum udp header (it should be in cache