load bucket policies using object layer API (#6084)

This PR fixes an issue during gateway mode
where underlying policies were not translated
into meaningful policies.

cmd/gateway-main.go

@@ -215,6 +215,13 @@ func StartGateway(ctx *cli.Context, gw Gateway) {
 		logger.FatalIf(err, "Unable to initialize gateway backend")
 	}
 
+	if gw.Name() != "nas" {
+		// Initialize policy sys for all gateways. NAS gateway already
+		// initializes policy sys internally, avoid double initialization.
+		// Additionally also don't block the initialization of gateway.
+		go globalPolicySys.Init(newObject)
+	}
+
 	// Once endpoints are finalized, initialize the new object api.
 	globalObjLayerMutex.Lock()
 	globalObjectAPI = newObject