BZ 56661: Fix Servlet API getLocalAddr().

Forward local IP address which is not part of AJP protocol
via custom request attribute named "AJP_LOCAL_ADDR".
Currently Tomcat will handle getLocalAddr(U) like getLocalName().

Tomcat versions can now check for the new attribute and use it
if available.

Likely to be used by forthcoming TC 6.0.41, 7.0.55 and 8.0.11.


git-svn-id: https://svn.apache.org/repos/asf/tomcat/jk/trunk@1609589 13f79535-47bb-0310-9956-ffa450edef68