correct unsynchronized #ifdef for netbsd setsockopt(IPV6_BINDV6ONLY).
correct unsynchronized #ifdef for netbsd setsockopt(IPV6_BINDV6ONLY).

MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame,MarginC/kame