C2SoftMpeg2Dec: disable keep threads active for entire sequence

Bug: 335786025
Test: atest android.mediav2.cts
      atest android.media.decoder.cts
      atest VtsHalMediaC2V1_0TargetVideoDecTest

Change-Id: I786716ce841812bd9d6d514a2ab61d00d4ad622e
diff --git a/media/codec2/components/mpeg2/Android.bp b/media/codec2/components/mpeg2/Android.bp
index a58044c..e644ee3 100644
--- a/media/codec2/components/mpeg2/Android.bp
+++ b/media/codec2/components/mpeg2/Android.bp
@@ -14,6 +14,10 @@
         "libcodec2_soft_sanitize_signed-defaults",
     ],
 
+    cflags: [
+        "-DKEEP_THREADS_ACTIVE=0",
+    ],
+
     srcs: ["C2SoftMpeg2Dec.cpp"],
 
     static_libs: ["libmpeg2dec"],