Make routingworker.hh public

Given that worker.hh was public, it made sense to make routingworker.hh
public as well. This removes the need to include private headers in
modules and allows C++ constructs to be used in C++ code when previously
only the C API was available.

server/modules/routing/debugcli/debugcmd.cc

@@ -54,6 +54,7 @@
 #include <maxscale/utils.h>
 #include <maxscale/version.h>
 #include <maxscale/routingworker.h>
+#include <maxscale/routingworker.hh>
 
 #include <debugcli.h>
 
@@ -65,7 +66,6 @@
 #include "../../../core/internal/poll.hh"
 #include "../../../core/internal/session.h"
 #include "../../../core/internal/filter.hh"
-#include "../../../core/internal/routingworker.hh"
 
 #define MAXARGS 14