Simplify code to preserve preferred APN across OTA update.

This also adds and keeps shared pref for longer to help debug
any issues. And includes a change to delete preferred APN ids
when APNs are deleted, as the ids may change after that.

Test: manual
Bug: 65132233
Change-Id: Ia5dab2bacc17bb6831ee80526f687cc6f56f7fc8
1 file changed