Set all T-Mobile and MetroPCS APNs to IPv6.

T-Mobile has requeested that the APN be set to IPv6 on all
MCC/MNC combinations, for both MetroPCs and T-Mobile. Currently
we only do IPv6 on MCC/MNC 310/160.

Also minor cleanups to some of the T-Mobile and MetroPCS APNs.

Bug: 9892287
Bug: 8612242
Change-Id: I6a742c18a239d37d52dc719638a9f46b2570a6a7