C2SoftAvcDec: Use a macro to control keep threads active flag

This change enables the keep threads active param
through a macro which makes it easier to change
when needed

Bug: 289097296
Test: atest android.mediav2.cts
      atest android.media.decoder.cts
      atest VtsHalMediaC2V1_0TargetVideoDecTest

Change-Id: I786716ce841812bd9d6d514a2ab61d00d5ad632e
diff --git a/media/codec2/components/avc/Android.bp b/media/codec2/components/avc/Android.bp
index a7ae85b..8ccb9ac 100644
--- a/media/codec2/components/avc/Android.bp
+++ b/media/codec2/components/avc/Android.bp
@@ -17,6 +17,10 @@
 
     static_libs: ["libavcdec"],
 
+    cflags: [
+        "-DKEEP_THREADS_ACTIVE=1",
+    ],
+
     srcs: ["C2SoftAvcDec.cpp"],
 
     export_include_dirs: ["."],