dnsdist: Subnets excluded from dynamic rules should not count towards thresholds

dnsdist: Subnets excluded from dynamic rules should not count towards thresholds

Until now we only looked at whether a subnet was excluded from dynamic rules
when deciding to insert a block. This introduced an issue when the dynamic
rules were configured to group clients into subnets via the `setMasks` directive,
because then queries received from an excluded client were still counted towards
the thresholds for the final subnet. For example, when grouping IPv4 clients
into `/24` subnets and excluding `192.0.2.1`, we would end up blocking the
whole `192.0.2.0/24` subnet if the number of queries or responses received
from `192.0.2.1` were over the threshold.
From now on excluded subnets will no longer count toward the thresholds.

Signed-off-by: Remi Gacogne <remi.gacogne@powerdns.com>