Don't unmute when answering a handover connection

We usually unmute the mic when a new call is answered. However, since
handovers go through the same code path, they'd get unmuted too. We want
to preserve the mute behavior from pre-handover, so add a special case
check.

Bug: 63795849
Test: manual
Change-Id: I7c09252d9541ab41c4bb72e5311e64d3c12b53ba