Allow merging of RTT calls based on carrier config

When the carrier config specifies it, allow RTT calls to be conferenced
with other calls.

Bug: 136035168
Test: manual

Change-Id: Ieacc342beff0ee51cad022a0b00ab1324ec8f3b4
Merged-In: Ieacc342beff0ee51cad022a0b00ab1324ec8f3b4
1 file changed