Fix gNMI-1.22 requirement for management port

[dplore]

The README currently specifies using a 'cpu' type interface, but the correct type is 'management.

[OpenConfigBot]

Pull Request Functional Test Report for #3364 / 0839be8d3a9de8d5e37018db73d0c8a148939da5

Virtual Devices

Device	Test	Test Documentation	Job	Raw Log
Arista cEOS		gNMI-1.22: Controller card port attributes	25f4f39d	Log
Cisco 8000E		gNMI-1.22: Controller card port attributes	58a1331f	Log
Cisco XRd		gNMI-1.22: Controller card port attributes	3b7513f8	Log
Juniper ncPTX		gNMI-1.22: Controller card port attributes	b6d0b30a	Log
Nokia SR Linux		gNMI-1.22: Controller card port attributes	65f16ab5	Log
Openconfig Lemming		gNMI-1.22: Controller card port attributes	f921da86	Log

Hardware Devices

Device	Test	Test Documentation	Raw Log
Arista 7808		gNMI-1.22: Controller card port attributes
Cisco 8808		gNMI-1.22: Controller card port attributes
Juniper PTX10008		gNMI-1.22: Controller card port attributes
Nokia 7250 IXR-10e		gNMI-1.22: Controller card port attributes

Help

[coveralls]

Pull Request Test Coverage Report for Build 10270657562

Details

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 55.5%

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Totals
Change from base Build 10268693714:	0.0%
Covered Lines:	1983
Relevant Lines:	3573

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💛 - Coveralls