Ensure that net_time filter isn't added on subreqs - we assume that it is

added on !r->main requests.  This led to infinite loop/SEGV when dealing
with anything that created a subreq.

(I don't think core_create_req is a good place for adding this filter.)


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@93694 13f79535-47bb-0310-9956-ffa450edef68