package/busybox: enable flags for use as systemd pager

If the less package is not enable and systemd is enabled,
then configure the less applet to fully work with systemd.

systemd sets the flags for less in an environment variable
and requires a few options for correct display.

Signed-off-by: Norbert Lange <nolange79@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>