Bug Template

Title: x-forwarded-proto gets overwritten when use_remote_address=true

Description:
When Envoy is deployed behind a trusted edge load balancer (in my case, it's provided by cloud vendor Aliyun.com), and correspondingly set xff_num_trusted_hops greater than 0, it should forward header x-forwarded-proto from downstream to upstream without modification. Even with use_remote_address set to true.

Repro steps:

See: https://github.com/5long/envoy-forwarded-proto with a working Docker Stack config to reproduce it.

Config:
It's included in the git repo above.