Enable inter-layer prediction by default in test apps.

This sets the default inter-layer prediction mode in the test
applications equal to the default value used by WebRTC sender:
- 2 (enabled only for key frames) for normal video.
- 0 (enabled for all frames) for screen sharing.

Bug: none
Change-Id: I1b60d3b906838d2c6f1bef3bb7f7d881bb43534e
Reviewed-on: https://webrtc-review.googlesource.com/78620
Reviewed-by: Michael Horowitz <mhoro@webrtc.org>
Reviewed-by: Erik Språng <sprang@webrtc.org>
Commit-Queue: Sergey Silkin <ssilkin@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#23446}