SEBA-499: Sending OLT Serial Number from BBSIM in GetDeviceInfo response. Also change sleep unit before the ONUIndication, from second to millisecond

Change-Id: I6783fabad1e0b6db923ded4f92073cadbc8eccd3
diff --git a/core/grpc_service.go b/core/grpc_service.go
index fe88a5a..5f927d9 100644
--- a/core/grpc_service.go
+++ b/core/grpc_service.go
@@ -18,6 +18,7 @@
 
 import (
 	"net"
+	"strconv"
 
 	"gerrit.opencord.org/voltha-bbsim/common/logger"
 	"gerrit.opencord.org/voltha-bbsim/common/utils"
@@ -70,6 +71,8 @@
 	devinfo.GemportIdEnd = 65535
 	devinfo.FlowIdStart = 1
 	devinfo.FlowIdEnd = 16383
+	devinfo.DeviceSerialNumber = "BBSIMOLT00"+strconv.FormatInt(int64(s.Olt.ID), 10)
+
 
 	return devinfo, nil
 }