info: Reduce safety limit to 50 ms

After reducing the DGA query separation to 100 ms, the DGA safety kick in and
limits the DGA frequency. This patch changes the safety limit to 50 ms (20 Hz).

Target: trunk
Request: 2.11
Request: 2.10
Require-notes: no
Require-book: no
Acked-by: Paul Millar <paul.millar@desy.de>
Patch: https://rb.dcache.org/r/7540/
(cherry picked from commit 8c295eeec9da72895b1994d44eebff7b522edee7)