udptunnels: Call handle_offloads after inserting vlan tag.

handle_offloads() calls skb_reset_inner_headers() to store
the layer pointers to the encapsulated packet. However, we
currently push the vlag tag (if there is one) onto the packet
afterwards. This changes the MAC header for the encapsulated
packet but it is not reflected in skb->inner_mac_header, which
breaks GSO and drivers which attempt to use this for encapsulation
offloads.

Fixes: 1eaa8178 ("vxlan: Add tx-vlan offload support.")
Signed-off-by: Jesse Gross <jesse@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/geneve.c b/net/ipv4/geneve.c
index 5a4828b..a566a2e 100644
--- a/net/ipv4/geneve.c
+++ b/net/ipv4/geneve.c
@@ -113,10 +113,6 @@
 	int min_headroom;
 	int err;
 
-	skb = udp_tunnel_handle_offloads(skb, csum);
-	if (IS_ERR(skb))
-		return PTR_ERR(skb);
-
 	min_headroom = LL_RESERVED_SPACE(rt->dst.dev) + rt->dst.header_len
 			+ GENEVE_BASE_HLEN + opt_len + sizeof(struct iphdr)
 			+ (skb_vlan_tag_present(skb) ? VLAN_HLEN : 0);
@@ -131,6 +127,10 @@
 	if (unlikely(!skb))
 		return -ENOMEM;
 
+	skb = udp_tunnel_handle_offloads(skb, csum);
+	if (IS_ERR(skb))
+		return PTR_ERR(skb);
+
 	gnvh = (struct genevehdr *)__skb_push(skb, sizeof(*gnvh) + opt_len);
 	geneve_build_header(gnvh, tun_flags, vni, opt_len, opt);