Don't allow CBRS subscriptions to be set as default for Calls/SMS

CBRS subscriptions (also known as "opportunistic" in the code base) are
data-only and it should not be possible to try to set them as the
default for Calls or SMS.

Fixes: 125855327
Test: make RunSettingsRoboTests
Change-Id: Ie20ef21ccc7b27315089f6a61cceb6e1512ec373