Try to clarify what client_ip/client_addr means

and point to useragent_ip.

Backport of r1331115 from trunk.

CTR because only comments.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1362122 13f79535-47bb-0310-9956-ffa450edef68