Description: Specifies the index of a port or a slot for traffic limitation. 
It uniquely identifies a port or a slot. 
The value and algorithm are the same as those of ifIndex. 

If the configuration based on a slot, the bits map is shown as follows:
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| 31-25 bits          | 24-19 bits         | 18-13 bits         | 12-6 bits            | 5-0 bits is reserved |
| indicate iftype     | indicate frame ID  | indicate slot ID   | indicate port ID     |                      |               
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| the value of iftype | frame ID           | slot ID            | the value of port ID | the reserved value   |
| is always 0x68      |                    |                    | is always 0          | is always 0          |
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Range: 0-4294967295