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>

net/l2tp/l2tp_ip.c

@@ -655,3 +655,4 @@ MODULE_VERSION("1.0");
  * enums
  */
 MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 2, IPPROTO_L2TP);
+MODULE_ALIAS_NET_PF_PROTO(PF_INET, IPPROTO_L2TP);

net/l2tp/l2tp_ip6.c

@@ -801,3 +801,4 @@ MODULE_VERSION("1.0");
  * enums
  */
 MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET6, 2, IPPROTO_L2TP);
+MODULE_ALIAS_NET_PF_PROTO(PF_INET6, IPPROTO_L2TP);