[IPV6]: Fix fallout from CONFIG_IPV6_PRIVACY

Trying to build today's 2.6.14+git snapshot gives undefined references
to use_tempaddr

Looks like an ifdef got left out.

Signed-off-by: Peter Chubb <peterc@gelato.unsw.edu.au>
Signed-off-by: David S. Miller <davem@davemloft.net>