Fix face local node numbering for hex elements

Currently, the local node numbering for faces is not set up correctly for hex elements. The function `face_local_num_int` receives the vertex numbers of the face and returns the local node numbers (corresponding to the hex numbering) for the face. The function attempts to use the vertex numbers as local node numbers which they are not (vertex `i` doesn't always correspond to local node `i`). This change obtains the vertex node numbers and uses them appropriately. This change will only affect elements of FAMILY_CUBE.