l2tp: Don't assign net->gen->ptr[] for pppol2tp_net_ops.

Commit fd558d18 ("l2tp: Split pppol2tp patch into separate l2tp and
ppp parts") converted net->gen->ptr[pppol2tp_net_id] in l2tp_ppp.c to
net->gen->ptr[l2tp_net_id] in l2tp_core.c.

Now the leftover wastes one entry of net->gen->ptr[] in each netns.

Let's avoid the unwanted allocation.
Signed-off-by: Kuniyuki Iwashima <kuniyu@amazon.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_ppp.c

@@ -1393,8 +1393,6 @@ static int pppol2tp_getsockopt(struct socket *sock, int level, int optname,
  * L2TPv2, we dump only L2TPv2 tunnels and sessions here.
  *****************************************************************************/
 
-static unsigned int pppol2tp_net_id;
-
 #ifdef CONFIG_PROC_FS
 
 struct pppol2tp_seq_data {
@@ -1628,7 +1626,6 @@ static __net_exit void pppol2tp_exit_net(struct net *net)
 static struct pernet_operations pppol2tp_net_ops = {
 	.init = pppol2tp_init_net,
 	.exit = pppol2tp_exit_net,
-	.id   = &pppol2tp_net_id,
 };
 
 /*****************************************************************************