Adjust the default gain in UI

Show a fixed full gain in UI before it really works per UX requirement.

Change-Id: I972cba2d74ce8a4880b4f5f02c52012b39f26dac
Bug: b/355684672, b/357123258
Test: atest InputRouteManagerTest
Flag: com.android.media.flags.enable_audio_input_device_routing_and_volume_control
2 files changed