fix(gateway): don't skip retry policy with retry methods (#6896)

1. The logic was wrong - if there is ***NO*** retry policy, we should
   skip applying retriable methods, not the other way around
2. Before it might crash with nil pointer dereference when we provided
   httpMethods, but there was no retry policy

Signed-off-by: Bart Smykla <bartek@smykla.com>

pkg/plugins/runtime/gateway/route/configurers.go

@@ -544,7 +544,7 @@ func RouteActionRetryMethods(httpMethod ...string) RouteConfigurer {
 
 	return RouteConfigureFunc(func(r *envoy_config_route.Route) error {
 		p := r.GetRoute().GetRetryPolicy()
-		if p != nil {
+		if p == nil {
 			return nil
 		}