Update Golang CI Lint to the latest version (#113)

This change updates Golang CI Lint to the latest version and fixes new
linter errors that came along with the update.

These changes were split out of #112 and are required to update the Go
version.

internal/controller/nbpolicy_controller.go

@@ -31,7 +31,7 @@ type NBPolicyReconciler struct {
 }
 
 var (
-	errUnknownProtocol = fmt.Errorf("Unknown protocol")
+	errUnknownProtocol = fmt.Errorf("unknown protocol")
 	errKubernetesAPI   = fmt.Errorf("kubernetes API error")
 	errNetBirdAPI      = fmt.Errorf("netbird API error")
 	errInvalidValue    = fmt.Errorf("invalid value")