meta: time: use uint64_t instead of time_t

meta: time: use uint64_t instead of time_t

time_t may be 32 bit on some platforms and thus can't fit a timestamp
with nanoseconds resolution. This causes overflows and ultimatively
breaks meta time expressions on such platforms.

Fix this by using uint64_t instead.

Closes: https://bugzilla.netfilter.org/show_bug.cgi?id=1567
Fixes: f8f32deda31df ("meta: Introduce new conditions 'time', 'day' and 'hour'")
Signed-off-by: Lukas Straub <lukasstraub2@web.de>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>