Minor perf improvement with exgws

On every pod add we assemble a new slice with all of the gatewayInfos.
This had no capacity, so every append was an underlying array copy.
Attempt to allocate at least some predictable capacity to avoid this.

Signed-off-by: Tim Rozet <trozet@redhat.com>

go-controller/pkg/ovn/pods.go

@@ -458,7 +458,7 @@ func (oc *Controller) addLogicalPort(pod *kapi.Pod) (err error) {
 	}
 
 	// if we have any external or pod Gateways, add routes
-	gateways := make([]*gatewayInfo, 0)
+	gateways := make([]*gatewayInfo, 0, len(routingExternalGWs.gws)+len(routingPodGWs))
 
 	if len(routingExternalGWs.gws) > 0 {
 		gateways = append(gateways, routingExternalGWs)