Werk #15175: Interface checks: re-work misleading bandwidth levels configuration

When configuring bandwidth levels, users previously configured

1. Traffic direction: in / out / both
2. Are the tresholds upper or lower thresholds?
3. Threshold type: absolute / relative to interface speed / predictive
4. Specific settings for selected threshold type

However, when selecting predictive levels, users had to again configure settings for upper and/or lower thresholds. In this case, the outer setting (number 2 from the list above) had no effect. Hence, the new configuration looks like this:

1. Traffic direction: in / out / both
2. Threshold type: absolute / relative to interface speed / predictive
3. Specific settings for selected threshold type, including upper/lower setting

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