mod_dumpio: do nothing below log level TRACE7.

For instance, depending on EnableMMAP/Sendfile configuration, don't split
file brigades to 8K heap buckets upon reading.



mod_dumpio: follow up to r1818802.

Negate APLOGctrace7(c) test!

Also, return DECLINED when nothing is to be done, same result as OK but
possibly more semantically correct.


Submitted by: ylavic
Reviewed by: jailletc36, jorton, ylavic


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1828743 13f79535-47bb-0310-9956-ffa450edef68