Adjust media buffer GC threshold

YouTube suggests 40 Mbps as maximum bitrate for 4k60p videos.
Reduce the GC threshold to keep buffer memory below 200 mb.

Change-Id: Ia4c8e700105c3160f5038c86d60e0062d6d65d8a

src/third_party/starboard/rdk/shared/media/media_get_buffer_garbage_collection_duration_threshold.cc

diff --git a/src/third_party/starboard/rdk/shared/media/media_get_buffer_garbage_collection_duration_threshold.cc b/src/third_party/starboard/rdk/shared/media/media_get_buffer_garbage_collection_duration_threshold.cc
index 4aa55ea..e8f872e 100644
--- a/src/third_party/starboard/rdk/shared/media/media_get_buffer_garbage_collection_duration_threshold.cc
+++ b/src/third_party/starboard/rdk/shared/media/media_get_buffer_garbage_collection_duration_threshold.cc
@@ -34,5 +34,5 @@
 #include "starboard/common/log.h"
 
 SbTime SbMediaGetBufferGarbageCollectionDurationThreshold() {
-  return 170 * kSbTimeSecond;
+  return 40 * kSbTimeSecond;
 }