Set withIgmp to true for TT scale tests with grpc images

Change-Id: I069875858366d857373116fc3586a0b6e7b8d2c0
diff --git a/jjb/voltha-scale.yaml b/jjb/voltha-scale.yaml
index 1f3ac62..8ff06fb 100644
--- a/jjb/voltha-scale.yaml
+++ b/jjb/voltha-scale.yaml
@@ -124,7 +124,7 @@
           provisionSubscribers: true
           withEapol: false
           withDhcp: true
-          withIgmp: false
+          withIgmp: true
           workflow: tt
           inMemoryEtcdStorage: false
           extraHelmFlags: >