totemknet: Handle new knet2 datafd API

If compiled against the new knet (KNET_DATAFD_FLAG_RX_RETURN_INFO)
then use the new 4-param knet_handle_add_datafd() API call.

Signed-off-by: Christine Caulfield <ccaulfie@redhat.com>
Reviewed-by: Jan Friesse <jfriesse@redhat.com>