[VOL-2356]core log_level command line argument should take log level names not int value

- StringToLogLevel method returns two arguments.

Change-Id: I83d20d645fa63363e71265b163273414f14688a7
diff --git a/go.mod b/go.mod
index 6a7728f..b4f685f 100644
--- a/go.mod
+++ b/go.mod
@@ -7,7 +7,7 @@
 	github.com/cenkalti/backoff/v3 v3.1.1
 	github.com/gogo/protobuf v1.3.1
 	github.com/golang/protobuf v1.3.2
-	github.com/opencord/voltha-lib-go/v3 v3.0.10
+	github.com/opencord/voltha-lib-go/v3 v3.0.12
 	github.com/opencord/voltha-protos/v3 v3.2.4
 	go.etcd.io/etcd v0.0.0-20190930204107-236ac2a90522
 	google.golang.org/grpc v1.25.1