Set X-Forwarded-Proto only if empty

ocp routes add these header based on ssl config,
let's honor that and set this request header only in
httpd config only if it's empty.

Noticed this issue with pagination tests when deployed
control plane with tls.podlevel=false and tls.ingress=true.

templates/neutronapi/httpd/10-neutron-httpd.conf

@@ -13,9 +13,9 @@
   ## Request header rules
   ## as per http://httpd.apache.org/docs/2.2/mod/mod_headers.html#requestheader
 {{- if $vhost.TLS }}
-  RequestHeader set X-Forwarded-Proto "https"
+  RequestHeader setIfEmpty X-Forwarded-Proto "https"
 {{- else }}
-  RequestHeader set X-Forwarded-Proto "http"
+  RequestHeader setIfEmpty X-Forwarded-Proto "http"
 {{- end }}
 
   ## Proxy rules