FreeBSD 8 does not have support for the TCP_KEEPIDLE, TCP_KEEPINTVL and
TCP_KEEPCNT options (the values are always hardcoded). We can fix it by only
calling setsockopt(2) with those options if they are defined.
At least for now, I have decided not to upstream this change because it
basically affects only FreeBSD 8 these days (the other BSDs, Linux and OS X
have had support for those options for many years).
MFH: 2014Q4
885c532f8e