Handle provisioning APN by turning off/on radio.

The change is specific to AT&T as they want no signaling from device during provisioning.
I've tested following cases:
- expired AT&T SIM to make sure provisioning flow works as expected.
- airplane mode on/off with both active and expired AT&T SIM.
- wifi <-> mobile transitions work okay.
- LTE with Verizon SIM (basic sanity).

bug: 13190133

Change-Id: I215963174ae6000ae71d1dda693f95413f3d6e81