its-g5: Use only the mandatory rates

Signed-off-by: Rostislav Lisovy <rostislav.lisovy@fel.cvut.cz>
its-g5: Change OCB housekeeping time intervals

The previous value was used for testing.
The new one is once again just guessed but is more aggressive
than the previous one.

Signed-off-by: Rostislav Lisovy <rostislav.lisovy@fel.cvut.cz>