Revert "net: ipv6/addrconf: clamp preferred_lft to the minimum required"

The commit had a bug and might not have been the right approach anyway.

Fixes: 629df670 ("net: ipv6/addrconf: clamp preferred_lft to the minimum required")
Fixes: ec575f88

 ("Documentation: networking: explain what happens if temp_prefered_lft is too small or too large")
Reported-by: Dan Moulding <dan@danm.net>
Closes: https://lore.kernel.org/netdev/20231221231115.12402-1-dan@danm.net/
Link: https://lore.kernel.org/netdev/CAMMLpeTdYhd=7hhPi2Y7pwdPCgnnW5JYh-bu3hSc7im39uxnEA@mail.gmail.com/


Signed-off-by: Alex Henrie <alexhenrie24@gmail.com>
Reviewed-by: David Ahern <dsahern@kernel.org>
Link: https://lore.kernel.org/r/20231230043252.10530-1-alexhenrie24@gmail.com


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