IPv6: only update the lifetime of the relevant temporary address

When receiving a prefix information from a routeur, only update the
lifetimes of the temporary address associated with that prefix.

Otherwise if one deprecated prefix is advertized, all your temporary
addresses will become deprecated.

Signed-off-by: Benoit Boissinot <benoit.boissinot@ens-lyon.org>
Acked-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>