DSDA: Update hold capability across subscriptions.

- When there are 2 calls across subs, they were each marked as holdable.
- When a 3rd MT call is accepted, the logic to terminate the bg call
  would not be triggered. Marking both calls as not holdable (but still
supports hold) solves the issue.

Bug: 280560635
Test: Live DSDA testing. Updated HoldTrackerTest.

Change-Id: I42785c42df51dab5e4bca0f447c019d9270f243a
3 files changed