AudioFlinger: input thread dump shows if RecordTrack is silenced

For each record thread, show if tracks are 's'ilenced
  or 'n'ormal

Bug: 70304055
Test: during recording: adb shell dumpsys media.audio_flinger
   look at active tracks under "Input thread"

Change-Id: I8b745bd5f8a9b6b228129dd8981acea7fb230acd