l2tp: Fix modalias of l2tp_ip

Using the SOCK_DGRAM enum results in
"net-pf-2-proto-SOCK_DGRAM-type-115", so use the numeric value like it
is done in net/dccp.
Signed-off-by: Michal Marek <mmarek@suse.cz>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ip.c

@@ -674,4 +674,8 @@ MODULE_LICENSE("GPL");
 MODULE_AUTHOR("James Chapman <jchapman@katalix.com>");
 MODULE_DESCRIPTION("L2TP over IP");
 MODULE_VERSION("1.0");
-MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, SOCK_DGRAM, IPPROTO_L2TP);
+
+/* Use the value of SOCK_DGRAM (2) directory, because __stringify does't like
+ * enums
+ */
+MODULE_ALIAS_NET_PF_PROTO_TYPE(PF_INET, 2, IPPROTO_L2TP);