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>

net/ipv4/af_inet.c

@@ -1258,6 +1258,7 @@ static struct sk_buff *inet_gso_segment(struct sk_buff *skb,
 		       SKB_GSO_SIT |
 		       SKB_GSO_TCPV6 |
 		       SKB_GSO_UDP_TUNNEL |
+		       SKB_GSO_UDP_TUNNEL_CSUM |
 		       SKB_GSO_MPLS |
 		       0)))
 		goto out;