initlvl=2 in seclvl gives the guarantee
"Cannot decrement the system time".

But it was possible to set the time to the maximum unixtime value
(19 Jan 2038) resulting in a wrap to the minimum value.

This patch fixes this by disallowing setting the time to any date
after 2030 with initlvl=2.
Signed-off-by: Adrian Bunk <bunk@stusta.de>