Support promotion of WFC.

Use new carrier config option to determine if the carrier wishes to promote
the user of Wifi Calling on call fail.'
If the user is on a WIFI network, and WFC is not enabled, and the carrier
wishes to promote the use of WIFI calling, display an alternate message
when calls fail, encouraging the user to enable wifi calling.

Bug: 27970317
Change-Id: Iecdda2dda13585307280c0e366fa6d84dba233c5
3 files changed