zebra, ripngd: remove ::/64 special-casing

zebra, ripngd: remove ::/64 special-casing

In the 90ies, IPv4 was believed to exist within IPv6, with some kernels
implementing this belief in code...  Our code here is keyed to "#ifdef
LINUX", yet no Linux from the past 10 years had this, making the code
completely useless.

FreeBSD 10.0 does in fact have a "::/96 via ::1 dev lo0 reject" route.
IMHO we shouldn't mess with that, the admin can filter as neccessary
anyway.

Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
Acked-by: Greg Troxel <gdt@ir.bbn.com>
Acked-by: Feng Lu <lu.feng@6wind.com>
[DL: slightly adjusted commit message to remove misunderstanding]
Acked-by: Paul Jakma <paul@jakma.org>