[VOL-3548] Differentiate between OLT gRPC channel disconnect and device reboot

- Return the previously_connected state flag in response to GetDeviceInfo to VOLTHA

Change-Id: I3a39eccdda386658226c6379a4815900b808795d
diff --git a/agent/src/core_api_handler.cc b/agent/src/core_api_handler.cc
index 3d8bd93..95a3a67 100644
--- a/agent/src/core_api_handler.cc
+++ b/agent/src/core_api_handler.cc
@@ -214,6 +214,7 @@
     openolt_read_sysinfo("Serial Number", serial_number);
     OPENOLT_LOG(INFO, openolt_log_id, "Fetched device serial number %s\n", serial_number);
     device_info->set_device_serial_number(serial_number);
+    device_info->set_previously_connected(state.previously_connected());
 
     char device_id[OPENOLT_FIELD_LEN];
     memset(device_id, '\0', OPENOLT_FIELD_LEN);