VOL-1325   confluent-kafka-python will throw exception after 100k messages

Change-Id: I23c7c68daa22fa327d63eab179f252762e8b456d
diff --git a/voltha/northbound/kafka/kafka_proxy.py b/voltha/northbound/kafka/kafka_proxy.py
index f0c58c7..4b53483 100644
--- a/voltha/northbound/kafka/kafka_proxy.py
+++ b/voltha/northbound/kafka/kafka_proxy.py
@@ -167,6 +167,9 @@
                     d =  deferToThread(self.kproducer.produce, topic, msg, key)
                     yield d
                     log.debug('sent-kafka-msg', topic=topic, msg=msg)
+                    # send a lightweight poll to avoid an exception after 100k messages.
+                    d1 = deferToThread(self.kproducer.poll, 0)
+                    yield d1
                 else:
                     return