Support restricting Listener address to `podIPs`

*Description*:
Right now it's a static "all addresses". Restricting to pod IPs would be much cleaner. Especially important if the gateway is running in `hostNetwork` mode where using all addresses can cause collisions.

Trace the Kubernetes gateway implementation for Listener address handling and pod IP discovery, then identify the existing tests covering listener binding. Add support for restricting a Listener to pod IPs, and verify that hostNetwork deployments no longer bind all addresses while existing listener behavior remains intact.

Written by the indexing model from the issue text.