tcp: further cleanup old options

[glebius]

Summary

They all were experimental and some comments refer to internal Netflix
versions. There is not reason to leak that into the header. Style unused
options so that they have the available value aligned with really used
values.

[glebius]

Internally at Netflix I will make all private options relative to TCP_VENDOR. This will make my merging much easier. Ideally we even want this to become a enum, and that would protect again any collisions and other failures.

[tuexen]

I was using the style used in netinet/in.h. But I do not care how we mark them as unused as long as it is consistent.

[tuexen]

In D46779#1066415, @glebius wrote:

Internally at Netflix I will make all private options relative to TCP_VENDOR. This will make my merging much easier. Ideally we even want this to become a enum, and that would protect again any collisions and other failures.

Using an enum will break the logic, if someone uses the pattern

#ifdef TCP_OPTION_NAME
....
#endif

I do this, for example, in symbols_freebsd.c for packetdrill.
One solution would be to use an enum and also #define. Not elegant...

sys/netinet/tcp.h

279

This is used by BBR.