[VOL-1501]  Ponsim OLT Adapter not receiving all packet out

This commit fixes that issue.  After Ponsim OLT Adapter sends a
PacketIn message, the twisted thread was stuck with receiving
other packetIns from the Ponsim OLT device and therefore was not
consuming messages from kafka.  This is fixed by removing the
yield on the southbound grpc message retrieval.

Change-Id: I3629853f6e342147cc357d861af0f95d0aafe27c
diff --git a/python/adapters/ponsim_olt/ponsim_olt.py b/python/adapters/ponsim_olt/ponsim_olt.py
index 4f5af65..fc617a3 100644
--- a/python/adapters/ponsim_olt/ponsim_olt.py
+++ b/python/adapters/ponsim_olt/ponsim_olt.py
@@ -399,7 +399,7 @@
             for frame in self.frames:
                 self.log.info('received-grpc-frame',
                               frame_len=len(frame.payload))
-                yield self._rcv_frame(frame.payload)
+                self._rcv_frame(frame.payload)
 
         except _Rendezvous, e:
             log.warn('grpc-connection-lost', message=e.message)