net: Infrastructure for CHECKSUM_PARTIAL with remote checsum offload

This patch adds infrastructure so that remote checksum offload can
set CHECKSUM_PARTIAL instead of calling csum_partial and writing
the modfied checksum field.

Add skb_remcsum_adjust_partial function to set an skb for using
CHECKSUM_PARTIAL with remote checksum offload.  Changed
skb_remcsum_process and skb_gro_remcsum_process to take a boolean
argument to indicate if checksum partial can be set or the
checksum needs to be modified using the normal algorithm.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/fou.c b/net/ipv4/fou.c
index 7fa8d36..d320f57 100644
--- a/net/ipv4/fou.c
+++ b/net/ipv4/fou.c
@@ -75,7 +75,7 @@
 		return NULL;
 	guehdr = (struct guehdr *)&udp_hdr(skb)[1];
 
-	skb_remcsum_process(skb, (void *)guehdr + hdrlen, start, offset);
+	skb_remcsum_process(skb, (void *)guehdr + hdrlen, start, offset, true);
 
 	return guehdr;
 }
@@ -230,7 +230,7 @@
 	}
 
 	skb_gro_remcsum_process(skb, (void *)guehdr + hdrlen,
-				start, offset, grc);
+				start, offset, grc, true);
 
 	skb->remcsum_offload = 1;