main/alpine-baselayout: move dad.if-up from busybox

The reason is that dad.if-up is also used by ifupdown-ng and therefor is misplaced in the busybox package (!61211 (comment 380080)).

I also moved all /etc/network/if-*.d directories to the alpine-baselayout package. Since ifupdown-ng properly handles missing /etc/network/if-*.d directories they could also be completely moved to the busybox package.