l2tp: close sessions before initiating tunnel delete

When a user deletes a tunnel using netlink, all the sessions in the tunnel
should also be deleted.  Since running sessions will pin the tunnel socket
with the references they hold, have the l2tp_tunnel_delete close all sessions
in a tunnel before finally closing the tunnel socket.

Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/l2tp/l2tp_core.c

@@ -1737,6 +1737,7 @@ EXPORT_SYMBOL_GPL(l2tp_tunnel_create);
  */
 int l2tp_tunnel_delete(struct l2tp_tunnel *tunnel)
 {
+	l2tp_tunnel_closeall(tunnel);
 	return (false == queue_work(l2tp_wq, &tunnel->del_work));
 }
 EXPORT_SYMBOL_GPL(l2tp_tunnel_delete);