Enable testing of WebRTC IP Permission Finch

testing/variations/fieldtrial_testing_config_mac.json

 {
     "AutofillClassifier": [
         {
             "group_name": "Enabled"
         }
     ],
     "AutofillFieldMetadata": [
         {
             "group_name": "Enabled"
         }
@@ skipping 124 matching lines @@
             "group_name": "DefaultEnabled"
         }
     ],
     "VarationsServiceControl": [
         {
             "group_name": "Interval_30min",
             "params": {
                 "fetch_period_min": "30"
             }
         }
+    ],
+    "WebRTC-LocalIPPermissionCheck": [
+        {
+            "group_name": "Enabled"
+        }
     ]
 }