C2SoftMpeg2Dec : Enable KEEP_THREADS_ACTIVE

Bug: 343793479
Test: atest MctsMediaV2TestCases
      atest MctsMediaDecoderTestCases
      atest MctsMediaCodecTestCases
      atest VtsHalMediaC2V1_0TargetVideoDecTest

Change-Id: I11eb3079281acb6a73ea9562b3e138373d9f8ebb
4 files changed