pkg-infra: do the package install before installing init files

The init hooks may reference files installed by the package. For
example, when a package installs systemd unit files, and wants them
enabled/disabled by default, the init hook may move/symlink/rename the
unit files.

Currently, the init hooks are called before the package is installed,
thus breaking the use-case above.

Just inverse the install order, so that a package is installed before
its init hooks are called.

Fixes: http://autobuild.buildroot.net/results/5b03174318d8a6dc3112053ff141b70a90869c20/



Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Eric Le Bihan <eric.le.bihan.dev@free.fr>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>