Optimization for core_output_filter: if the iovec is full,

don't try to concatenate buffers if we already have at least
8KB of data ready to send.  Instead, just split the brigade
and send what's currently in the iovec.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@92196 13f79535-47bb-0310-9956-ffa450edef68