Adding infrastructure to allow sending messages between adapters
using the adapter-agent event bus.

Change-Id: Ia3654b8944745bc76f8ac4ea3c1439a082979dd4
diff --git a/voltha/adapters/ponsim_onu/ponsim_onu.py b/voltha/adapters/ponsim_onu/ponsim_onu.py
index a131052..2098a22 100644
--- a/voltha/adapters/ponsim_onu/ponsim_onu.py
+++ b/voltha/adapters/ponsim_onu/ponsim_onu.py
@@ -143,6 +143,9 @@
         log.info('packet-out', logical_device_id=logical_device_id,
                  egress_port_no=egress_port_no, msg_len=len(msg))
 
+    def receive_inter_adapter_message(self, msg):
+        raise NotImplementedError()
+
 
 class PonSimOnuHandler(object):
     def __init__(self, adapter, device_id):