IP parameter added to ONU IGMP join/leave cli command

Change-Id: I1d821950deacba1d82d47731e644b917f3a6d7ed
diff --git a/internal/bbsim/devices/messageTypes.go b/internal/bbsim/devices/messageTypes.go
index e103ceb..144e1b9 100644
--- a/internal/bbsim/devices/messageTypes.go
+++ b/internal/bbsim/devices/messageTypes.go
@@ -139,6 +139,10 @@
 	GemPortId  uint32 // this is used by BBR
 }
 
+type IgmpMessage struct {
+	GroupAddress string
+}
+
 type OperState int
 
 const (