Backport r1476652:

Note that the buffer size is set to a maximum of 65536 when AJP is used as
per http://www.mail-archive.com/dev@httpd.apache.org/msg41843.html.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1476653 13f79535-47bb-0310-9956-ffa450edef68