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.

include/maxscale/session.hh

@@ -0,0 +1,38 @@
+/*
+ * Copyright (c) 2018 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2022-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+#pragma once
+
+#include <maxscale/utils.hh>
+
+namespace maxscale
+{
+/**
+ * Specialization of RegistryTraits for the session registry.
+ */
+template<>
+struct RegistryTraits<MXS_SESSION>
+{
+    typedef uint64_t id_type;
+    typedef MXS_SESSION* entry_type;
+
+    static id_type get_id(entry_type entry)
+    {
+        return entry->ses_id;
+    }
+    static entry_type null_entry()
+    {
+        return NULL;
+    }
+};
+
+}