udptunnel: Add SKB_GSO_UDP_TUNNEL during gro_complete.

commit cfdf1e1b upstream.

When doing GRO processing for UDP tunnels, we never add
SKB_GSO_UDP_TUNNEL to gso_type - only the type of the inner protocol
is added (such as SKB_GSO_TCPV4). The result is that if the packet is
later resegmented we will do GSO but not treat it as a tunnel. This
results in UDP fragmentation of the outer header instead of (i.e.) TCP
segmentation of the inner header as was originally on the wire.
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Ben Hutchings <ben@decadent.org.uk>
[ luis: backported to 3.16:
  - dropped changes to net/ipv4/fou.c
  - inlined call to udp_tunnel_gro_complete() in drivers/net/vxlan.c ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/net/vxlan.c

@@ -618,10 +618,15 @@ static int vxlan_gro_complete(struct sk_buff *skb, int nhoff)
 {
 	struct ethhdr *eh;
 	struct packet_offload *ptype;
+	struct udphdr *uh;
 	__be16 type;
 	int vxlan_len  = sizeof(struct vxlanhdr) + sizeof(struct ethhdr);
 	int err = -ENOSYS;
 
+	uh = (struct udphdr *)(skb->data + nhoff - sizeof(struct udphdr));
+	skb_shinfo(skb)->gso_type |= uh->check ?
+		SKB_GSO_UDP_TUNNEL_CSUM : SKB_GSO_UDP_TUNNEL;
+
 	eh = (struct ethhdr *)(skb->data + nhoff + sizeof(struct vxlanhdr));
 	type = eh->h_proto;