WebRTC-NetEqOpusDtxDelayFix: Add to fieldtrial configs

Adding the Enabled group, which is the intended launch config.

Bug: chromium:780849
Change-Id: I11a7c6074204a009cdb3b6204da2ed8a7c15a76a
Reviewed-on: https://chromium-review.googlesource.com/803271Reviewed-by: Mark Pearson <mpearson@chromium.org>
Commit-Queue: Henrik Lundin <hlundin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#521294}

testing/variations/fieldtrial_testing_config.json

@@ -4239,6 +4239,21 @@
             ]
         }
     ],
+    "WebRTC-NetEqOpusDtxDelayFix": [
+        {
+            "platforms": [
+                "chromeos",
+                "linux",
+                "mac",
+                "win"
+            ],
+            "experiments": [
+                {
+                    "name": "Enabled"
+                }
+            ]
+        }
+    ],
     "WebRTC-ProbingScreenshareBwe": [
         {
             "platforms": [