/** \brief Set or delete an GTPU tunnel
@param client_index - opaque cookie to identify the sender
@param context - sender context, to match reply w/ request
@param is_add - add address if non-zero, else delete
/** \brief Set or delete an GTPU tunnel
@param client_index - opaque cookie to identify the sender
@param context - sender context, to match reply w/ request
@param is_add - add address if non-zero, else delete