Complain if net.inet.ip.random_id is not set on FreeBSD-based servers

The attached patch lest Tor complain if net.inet.ip.random_id is not set on FreeBSD-based servers

Apparently a couple of operators haven't gotten the memos 0 yet and it looks like FreeBSD's default value will not change any time soon 1.

https://lists.torproject.org/pipermail/tor-relays/2014-November/005687.html https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=195828