Add missing import grpc

Change-Id: I488d3db9d4e8fb0a2eeb15766cc5725d1adf936b
diff --git a/voltha/adapters/openolt/openolt_data_model.py b/voltha/adapters/openolt/openolt_data_model.py
index 52bb511..58d2f75 100644
--- a/voltha/adapters/openolt/openolt_data_model.py
+++ b/voltha/adapters/openolt/openolt_data_model.py
@@ -325,6 +325,12 @@
             parent_port_no=self.platform.intf_id_to_port_no(intf_id,
                                                             Port.PON_OLT),
             onu_id=onu_id)
+
+        if onu_device is None:
+            self.log.error('onu_omci_rx: onu not found',
+                           intf_id=intf_id, onu_id=onu_id)
+            return
+
         self.adapter_agent.receive_proxied_message(onu_device.proxy_address,
                                                    pkt)
 
diff --git a/voltha/adapters/openolt/openolt_device.py b/voltha/adapters/openolt/openolt_device.py
index 4200428..a316e82 100644
--- a/voltha/adapters/openolt/openolt_device.py
+++ b/voltha/adapters/openolt/openolt_device.py
@@ -14,6 +14,7 @@
 # limitations under the License.
 #
 import binascii
+import grpc
 import structlog
 import time
 from scapy.layers.l2 import Ether, Dot1Q