/** \brief Add/del STN rules
@param client_index - opaque cookie to identify the sender
@param context - sender context, to match reply w/ request
/** \brief Add/del STN rules
@param client_index - opaque cookie to identify the sender
@param context - sender context, to match reply w/ request
@param ip_address - STN rule IP address
@param sw_if_index - Interface index
@param is_add - 1 if add, 0 if delete
@param ip_address - STN rule IP address
@param sw_if_index - Interface index
@param is_add - 1 if add, 0 if delete