The interface checks process a lot of different metrics (input and output bandwidth, input and
output error rates, input and and output packet rates, etc.). Before this werk, for any metric not
reported by a device, the interface checks returned constantly zero values. For example, for EC2
instances in AWS, the only metrics reported by the AWS special agent are input and output bandwidth.
Before this werk, the interface check constantly reported zero for all packet rates in this case.
This is however useless and potentially wrong in many places. Therefore, as of this werk, the
interface checks only return metrics for which the corresponding device actually reports values.
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