The attached patch set introduces L2TP support for Linux. There are now 
3 patches. These patches have been updated to include the changes requested.

ppp-add-pppol2tp-plugin.patch
Adds a pppol2tp plugin which lets pppd use the Linux pppol2tp.ko kernel 
driver to pass PPP frames in L2TP tunnels using PPPoL2TP sockets.

ppp-add-multilink-join-hook.patch
Adds a new hook: multilink_join_hook. This is called for multilink 
interfaces in start_networks() and allows plugins to be told when a new 
interface joins a multilink bundle. The openl2tp.so plugin previously 
used new_phase_hook to watch when new interfaces joined a bundle, but 
this new hook is a much cleaner way of achieving the same result.

ppp-add-openl2tp-plugin.patch
Adds an event interface which is used by the OpenL2TP implementation to 
  receive events from pppd using a Unix socket. Updated to use 
multilink_join_hook.

The L2TP plugins are being actively used by users of OpenL2TP and other 
L2TP daemons. Please consider for inclusion in the next release of pppd.

Thanks!

-- 
James Chapman
Katalix Systems Ltd
http://www.katalix.com
Catalysts for your Embedded Linux software development