l2tp: Add support for zero IPv6 checksums

Added new L2TP configuration options to allow TX and RX of
zero checksums in IPv6. Default is not to use them.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_core.h b/net/l2tp/l2tp_core.h
index 3f93ccd..68aa9ff 100644
--- a/net/l2tp/l2tp_core.h
+++ b/net/l2tp/l2tp_core.h
@@ -162,7 +162,9 @@
 #endif
 	u16			local_udp_port;
 	u16			peer_udp_port;
-	unsigned int		use_udp_checksums:1;
+	unsigned int		use_udp_checksums:1,
+				udp6_zero_tx_checksums:1,
+				udp6_zero_rx_checksums:1;
 };
 
 struct l2tp_tunnel {