Fix to return mno dun apn when mvno is not matched

If different type with same apn in apns-conf.xml,
apn should merge through createApnList() -> dedupeApnSettings()
but tethering apn will be chosen by fetchDunApn().
So, apn merge does not work in spite of using same apn.

This will cause make a another requestNetwork with same apn.
In this case, Hotspot is not working.

BUG=25331132

Change-Id: I43de74b93c919b0060b3ecc473b048f3c917e729