Revert "remove old apns-conf"

This reverts commit 2420e2a9719e8282bb4341937d20b1af1ee22a11.
d710.mk: add back in carrier property override
Revert "remove prebuilt apn config"

This reverts commit c4b9dec40e902809ec5b8f3b7d325c94cbbfa5ef.