Add getCapabilities to filters

Common capabilities are now defined in routing.h. The common
capabilities can be defined using bits 0 - 15.

Router capabilities are defined using bits 16-31 and filter
capabilities (should there ever be such) using bits 32-47.

So, to find out the capabilities of a service you only need to
OR the capabilities of the router and all filters together.

For instance, if a single filter needs statement based routing,
then that is what is done.

include/maxscale/routing.h

@@ -0,0 +1,38 @@
+#pragma once
+/*
+ * Copyright (c) 2016 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/bsl.
+ *
+ * Change Date: 2019-07-01
+ *
+ * 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.
+ */
+
+/**
+ * @file routing.h - Common definitions and declarations for routers and filters.
+ */
+
+#include <maxscale/cdefs.h>
+
+MXS_BEGIN_DECLS
+
+/**
+ * Routing capability type. Indicates what kind of input a router or
+ * a filter accepts.
+ *
+ * @note The values of the capabilities here *must* be between 0x0000
+ *       and 0x8000, that is, bits 0 to 15.
+ */
+typedef enum routing_capability
+{
+    RCAP_TYPE_STMT_INPUT = 0x0001, /**< Statement per buffer. */
+} routing_capability_t;
+
+#define RCAP_TYPE_NONE 0
+
+MXS_END_DECLS
+