[sonic-cfggen] sonic-cfggen should consider DPU ports when generating L2 mode configuration

[echuawu]

Description

When running L2 mode test on bobcat switch, the sonic-cfggen should consider the DPU ports.
Currently, when using command "sonic-cfggen -H -k Mellanox-SN4280-O28 -p --preset l2 > /tmp/init_l2_config.json", it would generate DPU ports with admin status UP, but the operation status would be DOWN.
The DPU ports configuration should be admin status DOWN, in order to make the L2 tests pass.

Steps to reproduce the issue:

1. On bobcat switch, run command "sonic-cfggen -H -k Mellanox-SN4280-O28 -p --preset l2 > /tmp/init_l2_config.json" to generate L2 mode port configuration.
2. Besides normal ports, the DPU ports would be admin status UP, and operation status DOWN.

Describe the results you received:

Ethernet224 224,225,226,227,228,229,230,231 400G 9100 N/A etp29 trunk down up DPU-NPU Data Port N/A
Ethernet232 232,233,234,235,236,237,238,239 400G 9100 N/A etp30 trunk down up DPU-NPU Data Port N/A
Ethernet240 240,241,242,243,244,245,246,247 400G 9100 N/A etp31 trunk down up DPU-NPU Data Port N/A
Ethernet248 248,249,250,251,252,253,254,255 400G 9100 N/A etp32 trunk down up DPU-NPU Data Port N/A

Describe the results you expected:

All the DPU ports configuration should be admin status DOWN.
Command "sonic-cfggen -H -k Mellanox-SN4280-O28 -p --preset l2" should handle the bobcat switch automatically.

Output of show version:

202405 image

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Output of show techsupport:

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