lineage: Disable IPv4 for T-Mobile (and MetroPCS) domestically

* T-Mobile's domestic network is IPv6 only, and T-Mobile
  support recommends setting IPv6 only for max compat
* T-Mobile support also recommends IPv4 only for roaming,
  however compat issues have been discovered in the past
* Switching to IPv6 only domestically fixes an issue with
  literal IPv4 addresses failing to resolve properly on ether

Change-Id: I7e394c6b7eebf9c106eaea5e000fe021adf421e6