Merge r280384 from trunk:

Document the ReceiveBufferSize change done in r157583
Submitted by: Murray Nesbitt <murray@cpan.org>

Submitted by: stas


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.0.x@371662 13f79535-47bb-0310-9956-ffa450edef68