Make RtpEncodingParameters to not reverse active flags order

Bug: webrtc:11319
Change-Id: If63db02d282ee622c12405f85c0fbae1ba13fcb2
Reviewed-on: https://webrtc-review.googlesource.com/c/src/+/168196
Reviewed-by: Florent Castelli <orphis@webrtc.org>
Commit-Queue: Ilya Nikolaevskiy <ilnik@webrtc.org>
Cr-Commit-Position: refs/heads/master@{#30459}
diff --git a/modules/video_coding/video_codec_initializer.cc b/modules/video_coding/video_codec_initializer.cc
index ea5de23..46d055f 100644
--- a/modules/video_coding/video_codec_initializer.cc
+++ b/modules/video_coding/video_codec_initializer.cc
@@ -156,6 +156,9 @@
       break;
     }
     case kVideoCodecVP9: {
+      // Force the first stream to always be active.
+      video_codec.simulcastStream[0].active = codec_active;
+
       if (!config.encoder_specific_settings) {
         *video_codec.VP9() = VideoEncoder::GetDefaultVp9Settings();
       }
@@ -197,7 +200,7 @@
              spatial_idx < config.simulcast_layers.size() &&
              spatial_idx < spatial_layers.size();
              ++spatial_idx) {
-          spatial_layers[spatial_layers.size() - spatial_idx - 1].active =
+          spatial_layers[spatial_idx].active =
               config.simulcast_layers[spatial_idx].active;
         }
       }