openvswitch: Fix GSO with multiple MPLS label.

MPLS GSO needs to know inner most protocol to process GSO packets.

Fixes: 25cd9ba0abc ("openvswitch: Add basic MPLS support to
kernel").

Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/openvswitch/actions.c b/net/openvswitch/actions.c
index 764fdc3..770064c 100644
--- a/net/openvswitch/actions.c
+++ b/net/openvswitch/actions.c
@@ -147,7 +147,8 @@
 	hdr = eth_hdr(skb);
 	hdr->h_proto = mpls->mpls_ethertype;
 
-	skb_set_inner_protocol(skb, skb->protocol);
+	if (!skb->inner_protocol)
+		skb_set_inner_protocol(skb, skb->protocol);
 	skb->protocol = mpls->mpls_ethertype;
 
 	invalidate_flow_key(key);