VOL-3344 - Enabled default linters and fixed found issues.

Also disabled govet's variable shadowing check, since this is very useful for isolating multiple "err"ors in a row.

Change-Id: Icd70c723c406c5986b8cfe4535ad7daa0752e48c
diff --git a/internal/pkg/core/statsmanager.go b/internal/pkg/core/statsmanager.go
index 6427a0c..53f81ab 100755
--- a/internal/pkg/core/statsmanager.go
+++ b/internal/pkg/core/statsmanager.go
@@ -288,12 +288,9 @@
 	metricNames := StatMgr.Device.metrics.GetSubscriberMetrics()
 
 	var metrics []string
-
-	if metricNames != nil && len(metricNames) > 0 {
-		for metric := range metricNames {
-			if metricNames[metric].Enabled {
-				metrics = append(metrics, metric)
-			}
+	for metric := range metricNames {
+		if metricNames[metric].Enabled {
+			metrics = append(metrics, metric)
 		}
 	}
 
@@ -332,12 +329,9 @@
 	metricNames := StatMgr.Device.metrics.GetSubscriberMetrics()
 
 	var metrics []string
-
-	if metricNames != nil && len(metricNames) > 0 {
-		for metric := range metricNames {
-			if metricNames[metric].Enabled {
-				metrics = append(metrics, metric)
-			}
+	for metric := range metricNames {
+		if metricNames[metric].Enabled {
+			metrics = append(metrics, metric)
 		}
 	}