l2tp: auto load IP modules

When creating a IP encapsulated tunnel the necessary l2tp module
should be loaded. It already works for UDP encapsulation, it just
doesn't work for direct IP encap.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/l2tp/l2tp_ip.c b/net/l2tp/l2tp_ip.c
index 7964993..ec22078 100644
--- a/net/l2tp/l2tp_ip.c
+++ b/net/l2tp/l2tp_ip.c
@@ -655,3 +655,4 @@
  * enums
  */
 MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 2, IPPROTO_L2TP);
+MODULE_ALIAS_NET_PF_PROTO(PF_INET, IPPROTO_L2TP);