Allow direct manipulation of streaming context parameters.

Added a method to change streaming context fragment unit and
size. The method has a side effect of resetting unit counter.

include/wsrep/client_state.hpp

@@ -305,6 +305,16 @@ namespace wsrep
                     transaction_.after_row() : 0);
         }
 
+        /**
+         * Set streaming parameters.
+         *
+         * @param fragment_unit Desired fragment unit
+         * @param fragment_size Desired fragment size
+         */
+        void streaming_params(enum wsrep::streaming_context::fragment_unit
+                              fragment_unit,
+                              size_t fragment_size);
+
         /**
          * Enable streaming replication.
          *