net: ipv6/addrconf: clamp preferred_lft to the maximum allowed

Without this patch, there is nothing to stop the preferred lifetime of a
temporary address from being greater than its valid lifetime. If that
was the case, the valid lifetime was effectively ignored.

Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231024212312.299370-2-alexhenrie24@gmail.com


Signed-off-by: Jakub Kicinski <kuba@kernel.org>