net: Kill link between CSUM and SG features.

Earlier SG was unset if CSUM was not available for given device to
force skb copy to avoid sending inconsistent csum.
Commit c9af6db4c11c (net: Fix possible wrong checksum generation)
added explicit flag to force copy to fix this issue.  Therefore
there is no need to link SG and CSUM, following patch kills this
link between there two features.

This patch is also required following patch in series.

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/core/skbuff.c b/net/core/skbuff.c
index 33245ef..0a48ae2 100644
--- a/net/core/skbuff.c
+++ b/net/core/skbuff.c
@@ -2741,12 +2741,19 @@
 	unsigned int tnl_hlen = skb_tnl_header_len(skb);
 	unsigned int headroom;
 	unsigned int len;
+	__be16 proto;
+	bool csum;
 	int sg = !!(features & NETIF_F_SG);
 	int nfrags = skb_shinfo(skb)->nr_frags;
 	int err = -ENOMEM;
 	int i = 0;
 	int pos;
 
+	proto = skb_network_protocol(skb);
+	if (unlikely(!proto))
+		return ERR_PTR(-EINVAL);
+
+	csum = !!can_checksum_protocol(features, proto);
 	__skb_push(skb, doffset);
 	headroom = skb_headroom(skb);
 	pos = skb_headlen(skb);
@@ -2884,6 +2891,12 @@
 		nskb->data_len = len - hsize;
 		nskb->len += nskb->data_len;
 		nskb->truesize += nskb->data_len;
+
+		if (!csum) {
+			nskb->csum = skb_checksum(nskb, doffset,
+						  nskb->len - doffset, 0);
+			nskb->ip_summed = CHECKSUM_NONE;
+		}
 	} while ((offset += len) < skb->len);
 
 	return segs;