tcp: remove tcptw, the compressed timewait state structure

[glebius]

Summary

The memory savings the tcptw brought back in 2003 no longer justify the
complexity required to maintain it. For longer explanation please check
out this email:

https://lists.freebsd.org/archives/freebsd-net/2022-January/001206.html

This change just removes tcptw and leaves INP_TIMEWAIT. The flag will
be removed in step 2. This makes it easier to review and possibly debug
the changes.

[bz]

Reading your summary, the reader is left with "and what do you do instead?" Would probably be good (here and in step 2) to explain somewhere what the expected path forward is as I am not assuming you are removing timewait functionality from TCP entirely?

[glebius]

In D36398#826783, @bz wrote:

Reading your summary, the reader is left with "and what do you do instead?" Would probably be good (here and in step 2) to explain somewhere what the expected path forward is as I am not assuming you are removing timewait functionality from TCP entirely?

Will improve commit message on next rebase or fixup of the patch.

[glebius]

Rebase, improve commit message.

[glebius]

Update the commit message, attempt 2.

[tuexen]

Just a thought for a follow-up cleanup: possibly get rid of tcp_timewait.c and move the functions left to other places.

[glebius]

Committed 0d7445193abc