mod_status: Use APR apr_time_as_msec() macro for

conversion from apr_time_t to milliseconds instead
of hard-coded division by 1000.

Backport of r1839780 from trunk.

Submitted by: rjung
Reviewed by: rjung, rpluem, jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1840032 13f79535-47bb-0310-9956-ffa450edef68