[IPV6] ADDRCONF: Don't generate temporary address for ip6-ip6 interface.

As far as I can remember, I was going to disable privacy extensions
on all "tunnel" interfaces.  Disable it on ip6-ip6 interface as well.

Also, just remove ifdefs for SIT for simplicity.

Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>