upstream connections: implement caching of interface table.

upstream connections: implement caching of interface table.

*Description*:
There are situations where knowing the local interface name of an upstream connection (https://github.com/envoyproxy/envoy/pull/19336) is useful debugging information. However, accessing that information usually requires syscalls that can become too expensive under load (https://github.com/envoyproxy/envoy/issues/19717).

Implement caching of interface table in order to provide the information without having to guard the behavior for only some use cases, and without incurring undue perf cost under load.