net: Add GSO support for UDP tunnels with checksum

Added a new netif feature for GSO_UDP_TUNNEL_CSUM. This indicates
that a device is capable of computing the UDP checksum in the
encapsulating header of a UDP tunnel.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv6/udp_offload.c b/net/ipv6/udp_offload.c
index b261ee8..79da8b3 100644
--- a/net/ipv6/udp_offload.c
+++ b/net/ipv6/udp_offload.c
@@ -63,6 +63,7 @@
 		if (unlikely(type & ~(SKB_GSO_UDP |
 				      SKB_GSO_DODGY |
 				      SKB_GSO_UDP_TUNNEL |
+				      SKB_GSO_UDP_TUNNEL_CSUM |
 				      SKB_GSO_GRE |
 				      SKB_GSO_IPIP |
 				      SKB_GSO_SIT |
@@ -76,7 +77,8 @@
 		goto out;
 	}
 
-	if (skb->encapsulation && skb_shinfo(skb)->gso_type & SKB_GSO_UDP_TUNNEL)
+	if (skb->encapsulation && skb_shinfo(skb)->gso_type &
+	    (SKB_GSO_UDP_TUNNEL|SKB_GSO_UDP_TUNNEL_CSUM))
 		segs = skb_udp_tunnel_segment(skb, features);
 	else {
 		/* Do software UFO. Complete and fill in the UDP checksum as HW cannot