SCF_SACK_PERMIT
tp->sack_enable = ISSET(sc->sc_fixflags, SCF_SACK_PERMIT);
if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT))
SET(sc->sc_fixflags, SCF_SACK_PERMIT);
(ISSET(sc->sc_fixflags, SCF_SACK_PERMIT) ? 4 : 0) +
if (ISSET(sc->sc_fixflags, SCF_SACK_PERMIT)) {