Merge r1634120 from trunk:

* Use the correct server name for SNI in case the backend SSL connection itself
  is established via a proxy server.

PR: 57139
Submitted by: Szabolcs Gyurko <szabolcs gyurko.org>



git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1673941 13f79535-47bb-0310-9956-ffa450edef68