cve-update-db-native: update the CVE database once a day only

cve-update-db-native: update the CVE database once a day only

The update of the NVD database was expected to happen once per hour.
However, the database file date changes only if the content was actually
updated. In practice, the check worked for the first hour after the
new download.

As the NVD database changes usually only once a day, we can just
update it less frequently.

Signed-off-by: Marta Rybczynska <marta.rybczynska@huawei.com>
Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>