Werk #4766: snmp_extended_info: Inventorizes all available physical components except ports in more robust way

Note: Some bogus devices such as Cisco WLC 2500 Series or Cisco Wide Area Application Services either do not have exactly one entry == "0" which means device itself or do not provide any information about physical class. In the first case {{Hardware > System}} will be omitted. In the second case we inventorize these components below physical components table {{Unknown entities}}. In all cases ports are ignored because we have an extra view for them.

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