L2TP_HDR_CTRL
is_ctrl = (hdr & L2TP_HDR_CTRL) != 0;
if ((hdr & L2TP_HDR_CTRL) == 0) {
#define L2TP_CTRL_HDR (L2TP_HDR_CTRL | L2TP_HDR_LEN \
if ((hdr & L2TP_HDR_CTRL) != 0) {