TCP_SACK_PERMITTED
if ((segment.options & TCP_SACK_PERMITTED) == 0) {
segment.options |= TCP_SACK_PERMITTED;
if ((segment.options & TCP_SACK_PERMITTED) != 0) {
} else if ((segment.options & TCP_SACK_PERMITTED) != 0
segment.options |= TCP_SACK_PERMITTED;
else if ((segment.options & TCP_SACK_PERMITTED) != 0)