include/package-pack: actually call default_postinist/prerm when using APK

include/package-pack: actually call default_postinist/prerm when using APK

Currently, when you install a package that ships uci-defaults scripts they
are not getting executed during package installation.

For example, if you install a new LuCI theme it ships a uci-defaults script
to add it to the UCI LuCI config so the theme is actually selectable but
that does not happen until the device is rebooted so that uci-defaults
script is actually executed.

It turns out that the recipe for post-install is the issue since it will
include contents of postinst-pkg before the call to default_postinist.
This is an issue since postinst-pkg will exit with code 0 before we ever
reach the call to default_postinist.

So, lets simply make the call to default_postinist before postinst-pkg
inclusion which is what OPKG based installation does.

The same issue affects pre-deinstall script but its not actually being hit
since we dont seem to be actually even generating prerm-pkg scripts but
lets fix this theoretical issue as well.

Fixes: #16987
Fixes: d788ab376f85 ("build: add APK package build capabilities")
Link: https://github.com/openwrt/openwrt/pull/17023
Signed-off-by: Robert Marko <robimarko@gmail.com>