Mark RTT calls as non-conferenceable

In refreshConferenceSupported, check if the call is RTT and mark it
non-conferenceable if so. Also call refreshConferenceSupported when the
RTT status changes.

Bug: 109763648
Test: manual
Change-Id: I374b737d4f5dabec3091fb2da2eaf8355d54d221
1 file changed