ResolveRequest and the panel's resolveHost fell back to X-Real-IP for the host when a trusted proxy sent no X-Forwarded-Host. X-Real-IP names the visitor, so behind nginx with only that header set, subscription and exported links advertised the subscriber's own public IP as the server.
The host now comes from a trusted X-Forwarded-Host, else the dialed request Host. X-Real-IP stays a client-IP source only.
Fixes#6589.