Fix format pattern (%lu => %APR_SIZE_T_FMT).

Detected by maintainer mode compilation and GCC error:

.../modules/metadata/mod_remoteip.c:
In function 'remoteip_input_filter':
.../include/http_log.h:117:33:
error: format '%lu' expects argument of type
'long unsigned int', but argument 8 has type
'apr_size_t {aka unsigned int}' [-Werror=format=]


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@1812332 13f79535-47bb-0310-9956-ffa450edef68