BUG/MEDIUM: fix previousMapPort2Listeners never populated in resetListenerConflicts

resetListenerConflicts was resetting both mapPort2Listeners and
previousMapPort2Listeners to empty maps. As a result,
previousGatewaysWithPortConflicts() always returned an empty set, making
checkListenerConflicts unable to detect Gateways whose conflicts had been
resolved since the previous reconciliation cycle.

When a conflicting Gateway was deleted, the surviving Gateway would not be
added to the update list for reprocessing and would retain its conflict
condition in Kubernetes status indefinitely.

Fix by saving the current mapPort2Listeners into previousMapPort2Listeners
before resetting the current map, so that the previous conflict state is
correctly preserved across reconciliation cycles.

Author: ivanmatmati

k8s/gate/tree/gateway_builder.go

@@ -196,8 +196,8 @@ func (b *GatewayBuilderImpl) buildListeners(treeGw *Gateway) {
 }
 
 func (b *GatewayBuilderImpl) resetListenerConflicts() {
+	b.ControllerStore.previousMapPort2Listeners = b.ControllerStore.mapPort2Listeners
 	b.ControllerStore.mapPort2Listeners = make(map[gatewayv1.PortNumber]listenerConflict)
-	b.ControllerStore.previousMapPort2Listeners = make(map[gatewayv1.PortNumber]listenerConflict)
 }
 
 // checkListenerConflicts checks the conflicts between all Gateway listeners