Werk #15172: Interface checks: Fix rare interface mixups

In rare cases, the interface checks associated multiple interfaces with a given service item. Depending on the exact plugin, this could lead to incorrect monitoring results (wrong data or misleading failures in rate computations).

This happened if there was an interface where the combination of alias or description plus index matched the alias or description (without the index) of another interface. For example, the following combination lead to such as mixup:

• Item: Ethernet 2
• Interface 1: Index 1, Description Ethernet 2
• Interface 2: Index 2, Description Ethernet

In this case, Checkmk associated both interfaces with the item Ethernet 2, resulting in wrong monitoring results.

Furthermore, another potential side effect of this issue was that the Perf-O-Meters of affected services crashed with

Exception: list index out of range

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