It seems, that handling of DEFAULT_PACKAGES is needed in more places, so
lets move it into dedicated include file so it can be easily shared.
Signed-off-by: Petr Štetiar <ynezz@true.cz>
Link: https://github.com/openwrt/openwrt/pull/16986
Signed-off-by: Robert Marko <robimarko@gmail.com>
(cherry picked from commit 40be892a02)
