meta: fix hour decoding when timezone offset is negative

meta: fix hour decoding when timezone offset is negative

Brian Davidson says:

 meta hour rules don't display properly after being created when the
 hour is on or after 00:00 UTC. The netlink debug looks correct for
 seconds past midnight UTC, but displaying the rules looks like an
 overflow or a byte order problem. I am in UTC-0400, so today, 20:00
 and later exhibits the problem, while 19:00 and earlier hours are
 fine.

meta.c only ever worked when the delta to UTC is positive.
We need to add in case the second counter turns negative after
offset adjustment.

Also add a test case for this.

Fixes: f8f32deda31d ("meta: Introduce new conditions 'time', 'day' and 'hour'")
Reported-by: Brian Davidson <davidson.brian@gmail.com>
Signed-off-by: Florian Westphal <fw@strlen.de>