[MeL] Node: Constify parameter 'connected_nodes'.

MeshLib/Node.h

@@ -91,7 +91,7 @@ protected:
 
     /// Resets the connected nodes of this node. The connected nodes are
     /// generated by Mesh::setNodesConnectedByElements().
-    void setConnectedNodes(std::vector<Node*> &connected_nodes)
+    void setConnectedNodes(std::vector<Node*> const& connected_nodes)
     {
         _connected_nodes = connected_nodes;
     }