db/config.site cache for ac_cv_header_netinet_tcp_var_h

db/config.site has this:

1.6 (espie 24-Feb-05): ac_cv_header_netinet_tcp_timer_h=${ac_cv_header_netinet_tcp_timer_h=yes}

turns out this is a bit problematic, because on OpenBSD you need to
pull in tcp_timer.h before you can use tcp_var.h ("use of undeclared
identifier 'TCPT_NTIMERS'").

I wonder if we should remove this - at least one port (net/scamper)
has a patch to disable use of tcp_var.h because of this. (This was
figured out by scamper's developer who was wondering why I needed
to patch it).