fortune - Add a fun tip

* Works best with cowsay.
token.9: lwkt_token_init()'s desc argument is const.
dsched.9: Fix dsched_new_policy_thread_io()'s prototype (see 5374d04f).
inet6: Add missing ifioctl credential checks

This fixes issue #2581 (again), but with SIOCSIFBRDADDR and
SIOCSIFNETMASK ioctls this time.

Security: CVE-2013-5691
Patch-from: Loganaden Velvindron, inspired by FreeBSD changes