Merge branch 'l2tp-replace-custom-logging-code-with-tracepoints'

Tom Parkin says:

====================
l2tp: replace custom logging code with tracepoints

The l2tp subsystem implemented custom logging macros for debugging
purposes which were controlled using a set of debugging flags in each
tunnel and session structure.

A more standard and easier-to-use approach is to use tracepoints.

This patchset refactors l2tp to:

 * remove excessive logging
 * tweak useful log messages to use the standard pr_* calls for logging
   rather than the l2tp wrappers
 * replace debug-level logging with tracepoints
 * add tracepoints for capturing tunnel and session lifetime events

I note that checkpatch.pl warns about the layout of code in the
newly-added file net/l2tp/trace.h.  When adding this file I followed the
example(s) of other tracepoint files in the net/ subtree since it seemed
preferable to adhere to the prevailing style rather than follow
checkpatch.pl's advice in this instance.  If that's the wrong
approach please let me know.

v1 -> v2

 * Fix up a build warning found by the kernel test robot
====================

Signed-off-by: David S. Miller <davem@davemloft.net>