MXS-1406 Report CALL operation

Basically it would be trivial to report far more operations
explicitly, but for the fact that the values in qc_query_op_t
currently, quite unnecessarily, form a bitmask.

In 2.2 that is no longer the case, so other operations will be
added there.

include/maxscale/query_classifier.h

@@ -94,7 +94,8 @@ typedef enum qc_query_op
     QUERY_OP_CHANGE_DB     = (1 << 8),
     QUERY_OP_LOAD          = (1 << 9),
     QUERY_OP_GRANT         = (1 << 10),
-    QUERY_OP_REVOKE        = (1 << 11)
+    QUERY_OP_REVOKE        = (1 << 11),
+    QUERY_OP_CALL          = (1 << 12),
 } qc_query_op_t;
 
 /**