[yang] vlan subintf name does not match yang model definition

[ganglyu]

Description

Yang model does not support long name format for portchannel.

libyang[0]: Must condition "(substring-before(current(), '.') = /sonic-port:sonic-port/sonic-port:PORT/sonic-port:PORT_LIST/sonic-port:name) or (starts-with(substring-before(current(), '.'), 'Eth') and concat('Ethernet', substring-after(substring-before(current(), '.'), 'Eth')) = /sonic-port:sonic-port/sonic-port:PORT/sonic-port:PORT_LIST/sonic-port:name) or (starts-with(substring-before(current(), '.'), 'Po') and concat('PortChannel', substring-after(substring-before(current(), '.'), 'Po')) = /sonic-portchannel:sonic-portchannel/sonic-portchannel:PORTCHANNEL/sonic-portchannel:PORTCHANNEL_LIST/sonic-portchannel:name)" not satisfied. (path: /sonic-vlan-sub-interface:sonic-vlan-sub-interface/VLAN_SUB_INTERFACE/VLAN_SUB_INTERFACE_LIST[name='PortChannel01.10']/name)
libyang[0]: Must condition not satisfied, please follow vlan sub interface naming convention (path: /sonic-vlan-sub-interface:sonic-vlan-sub-interface/VLAN_SUB_INTERFACE/VLAN_SUB_INTERFACE_LIST[name='PortChannel01.10']/name)

Steps to reproduce the issue:

1. Create vlan subintf on portchannel
2. Run Yang validation

Describe the results you received:

Configurations generated from minigraph can't pass yang validation.

Describe the results you expected:

Configurations generated from minigraph should pass yang validation.

Output of show version:

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Output of show techsupport:

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Additional information you deem important (e.g. issue happens only occasionally):

[ganglyu]

Need to modify unit test to use 15 characters long sub interface name, related test cases are:
test_minigraph_storage_backend_no_resource_type
test_minigraph_sub_port_interfaces
test_minigraph_sub_port_intf_resource_type