WebSocket config: Fix `headers` (#4177)

Fixes https://github.com/XTLS/Xray-core/issues/4176

infra/conf/transport_internet.go

@@ -165,12 +165,14 @@ func (c *WebSocketConfig) Build() (proto.Message, error) {
 	}
 	// Priority (client): host > serverName > address
 	for k, v := range c.Headers {
+		if strings.ToLower(k) == "host"{
 			errors.PrintDeprecatedFeatureWarning(`"host" in "headers"`, `independent "host"`)
 			if c.Host == "" {
 				c.Host = v
 			}
 			delete(c.Headers, k)
 		}
+	}
 	config := &websocket.Config{
 		Path:                path,
 		Host:                c.Host,