Add module level static capabilities

The static capabilities declared in getCapabilities allows certain
capabilities to be queried before instances are created. The intended use
of this capability is to remove the need for the `is_internal_service`
function.

examples/roundrobinrouter.cpp

@@ -607,6 +607,7 @@ MXS_MODULE* MXS_CREATE_MODULE()
         MXS_ROUTER_VERSION,      /* Implemented module API version */
         "A simple round robin router", /* Description */
         "V1.1.0", /* Module version */
+        MXS_NO_MODULE_CAPABILITIES,
         &entryPoints, /* Defined above */
         process_init, /* Process init, can be null */
         process_finish, /* Process finish, can be null */