VOL-1494: Add missing field for ofp_stats

Copied over from voltha 1.x protos. Needed
by ofagent

Change-Id: I43ad2c918f309f7d1c5d1f5996154bf2f13df578
diff --git a/protos/voltha_protos/logical_device.proto b/protos/voltha_protos/logical_device.proto
index 6e3a233..f5e2fd8 100644
--- a/protos/voltha_protos/logical_device.proto
+++ b/protos/voltha_protos/logical_device.proto
@@ -22,6 +22,7 @@
     string device_id = 3;
     uint32 device_port_no = 4;
     bool root_port = 5;
+    openflow_13.ofp_port_stats ofp_port_stats = 6;
 }
 
 message LogicalPorts {