l2tp: Call udp_sock_create

In l2tp driver call common function udp_sock_create to create the
listener UDP port.

Signed-off-by: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/Kconfig b/net/l2tp/Kconfig
index adb9843..378c73b 100644
--- a/net/l2tp/Kconfig
+++ b/net/l2tp/Kconfig
@@ -6,6 +6,7 @@
 	tristate "Layer Two Tunneling Protocol (L2TP)"
 	depends on (IPV6 || IPV6=n)
 	depends on INET
+	select NET_UDP_TUNNEL
 	---help---
 	  Layer Two Tunneling Protocol