mod_cache_socache: Add cache status to server-status.

The status_hook simply calls the status function of
socache, very much like mod_ssl does for the ssl
session cache.


Silence build warning about missing prototype.
Followup to r1629507.

Submitted by: rjung
Reviewed/backported by: jim


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/branches/2.4.x@1634527 13f79535-47bb-0310-9956-ffa450edef68