tcp: remove IS_FASTOPEN() macro

[glebius]

Summary

The macro is more obfuscating than helping as it just checks a single flag
of t_flags. All other t_flags bits are checked without a macro.

A bigger problem was that declaration of the macro in tcp_var.h depended
on a kernel option. It is a bad practice to create such definitions in
installable headers.

[rscheff]

only minor whitespace nits. i'm ok with removing this macro mechanistically.

sys/netinet/tcp_output.c

244–245

why remove the newline here? I'd leave the individual check one per line, or concatenate the deeper bracketed OR together to a single line.
(minor nit-pick).

sys/netinet/tcp_stacks/rack.c

21952–21953

same.

22079

same.

[glebius]

Add back new lines as Richard suggests.

[rscheff]

thx

[kib]

I do not understand the change. You re-wrote the code as if the TCP_RFC7413 option is always set. This is not true, at least from the fast grepping of the sources.

[glebius]

In D44362#1011765, @kib wrote:

I do not understand the change. You re-wrote the code as if the TCP_RFC7413 option is always set. This is not true, at least from the fast grepping of the sources.

If kernel is compiled w/o the option, then t_flags & TF_FASTOPEN will always be false.

[rscheff]

In D44362#1011765, @kib wrote:

I do not understand the change. You re-wrote the code as if the TCP_RFC7413 option is always set. This is not true, at least from the fast grepping of the sources.

But the t_flag will be zeroed in all instances where FASTOPEN is not used or compiled in, thus functionally equivalent to returning false (as the old macro returned for userspace, and when TCP_RFC7413 was not set...

[glebius]

Committed dd7b86e2a010818b53f42200815f1858300045d7