l2tp: Refactor l2tp core driver to make use of the common UDP tunnel functions
l2tp: Refactor l2tp core driver to make use of the common UDP tunnel functions

Simplify l2tp implementation using common UDP tunnel APIs.

Signed-off-by: Andy Zhou <eba59be6f07811efcfb9b9013eddeb3628e492b2@nicira.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs