mod_http2: fixes timeout vs. keepalive timeout use when closing streams on...

mod_http2: fixes timeout vs. keepalive timeout use when closing streams on flush, adding pseudo header length check against limit_req_line

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1744415 13f79535-47bb-0310-9956-ffa450edef68