NEXTGEN APN  for AT&T D850

This line should be added to vendor/cm/prebuilt/common/etc/apns-conf.xml

<apn carrier="ATT Nextgenphone" mcc="310" mnc="410" apn="nxtgenphone" mmsc="http://mmsc.mobile.att.net" mmsproxy="proxy.mobile.att.net" mmsport="80" protocol="IP" type="default,mms,supl,hipri" />