Systemd-based systems do not use the global /etc/sysctl.conf file. Instead,
they read configuration from individual files under /etc/sysctl.d. This
change installs our sysctl settings as /etc/sysctl.d/console.conf when
systemd is enabled.
For systems that do not use systemd, the configuration file is still
installed at /etc/sysctl.conf. The CONFFILES entry is also updated.
Signed-off-by: Javier Viguera <javier.viguera@digi.com>