TOF_SACK_PERMITTED
if (tcp_do_sack && (to.to_flags & TOF_SACK_PERMITTED))
to->to_flags |= TOF_SACK_PERMITTED;
if (tcp_do_sack && (to->to_flags & TOF_SACK_PERMITTED))
if (tcp_do_sack && (to->to_flags & TOF_SACK_PERMITTED))