rename struct krb5_name_canon_* name collisions

C++ does not permit struct names and typedef names to be the same.
Rename

  struct krb5_name_canon_rule to struct krb5_name_canon_rule_data

and

  struct krb5_name_canon_iterator to struct krb5_name_canon_iterator_data

Change-Id: I92766e0878bf0beef92de1649baf9e5cafbf86aa