New ATT Nextgenphone APN

Change-Id: Ibd5794d248b8d5bf8d34cebe01686406f8e68e36

Easiest way to fix the APN issue with the new ATT APN and merging it into the CM apns-conf.xml file. If one merges the new APN into CM APN config file then it still causes issues for users. If you delete older APNs from CM file then it may cause issues with other devices.
Best way is to just use proper APN file in vendor setup.