Update to v4.15 kernel headers.

Test: NA.
Change-Id: Ic06b0506705a46ed11e3b9f212515d34147c8135
diff --git a/original/uapi/linux/if_tunnel.h b/original/uapi/linux/if_tunnel.h
index 383b850..e68dadb 100644
--- a/original/uapi/linux/if_tunnel.h
+++ b/original/uapi/linux/if_tunnel.h
@@ -85,6 +85,7 @@
 	TUNNEL_ENCAP_NONE,
 	TUNNEL_ENCAP_FOU,
 	TUNNEL_ENCAP_GUE,
+	TUNNEL_ENCAP_MPLS,
 };
 
 #define TUNNEL_ENCAP_FLAG_CSUM		(1<<0)