remove building kernel module, it is not used and is not working with 4.19

rework the ready to use l2tp-ipsec example

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>

use the kernel arch for building the modules

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>

Libreswan is a free software implementation of the most widely
supported and standardized VPN protocol based on ("IPsec") and
the Internet Key Exchange ("IKE"). These standards are produced
and maintained by the Internet Engineering Task Force ("IETF").

Signed-off-by: Lucian Cristian <lucian.cristian@gmail.com>