Hi, this is a patch to add TCPOPT and TCPOLEN constants to
netinet/tcp.h.

This was discussed in IRC a little, but upon me finishing it
it seemed to get lost in the noise. As such I've submitted it
here so that it won't get lost.

These constants are used by programs such as iptables and are
expected to be defined in the libc's tcp.h; glibc and BSD libcs
all have them exposed by default. However, they are not part of
tcp.h's reserved namespace, therefore it has been hidden behind
_BSD_SOURCE (which is the same as _DEFAULT_SOURCE internally)
so that the behavior is the same across other C libraries and
doesn't require patches to programs, but still manages to be
standards conforming if need be.

I've attached it since I don't trust gmail to not mess up patch
formatting.