When UpstreamEnvoyExtender was introduced, some code was left duplicated
between it and BasicEnvoyExtender. One path in that code panics when a
TProxy listener patch is attempted due to no upstream data in
RuntimeConfig matching the local service (which would only happen in
rare cases).
Instead, we can remove the special handling of upstream VIPs from
BasicEnvoyExtender entirely, greatly simplifying the listener filter
patch code and avoiding the panic. UpstreamEnvoyExtender, which needs
this code to function, is modified to ensure a panic does not occur.
This also fixes a second regression in which the Lua extension was not
applied to TProxy outbound listeners.
R.B. Boyer