include/package-pack: add special handling for CONTROL conffiles

include/package-pack: add special handling for CONTROL conffiles

Add special handling for CONTROL conffiles. Some packages (base-files)
manually append stuff to the CONTROL directory.

The CONTROL directory is something for OPKG that is added in the root of
the ipkg directory and usually contains postinst, list, and conffiles
file. For APK the implementation is different, to keep compatibility
with this and maybe other packages, apply manual fixup and check for
these corner case.

Also check if the CONTROL directory is present and is empty to make sure
we don't drop other special file while removing any pending CONTROL
directory in the ipkg directory.

Link: https://github.com/openwrt/openwrt/pull/15543
Signed-off-by: Christian Marangi <ansuelsmth@gmail.com>