Merge branch 'l2tp-miscellaneous-cleanups'

Tom Parkin says:

====================
l2tp: miscellaneous cleanups

This series of patches makes the following cleanups and improvements to
the l2tp code:

 * various API tweaks to remove unused parameters from function calls
 * lightly refactor the l2tp transmission path to capture more error
   conditions in the data plane statistics
 * repurpose the "magic feather" validation in l2tp to check for
   sk_user_data (ab)use as opposed to refcount debugging
 * remove some duplicated code
====================

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