[Yang] MACSEC_PROFILE table does not match yang definition

[ganglyu]

Description

MACSEC_PROFILE table is:
"MACSEC_PROFILE": {"128_SCI": {"cipher_suite": "GCM-AES-128", "policy": "security", "primary_cak": "3106080a00005b554f4e007975707670725b0a54540c0252445e5d7a29252b046a", "primary_ckn": "6162636465666768696A6B6C6D6E6F70", "priority": "64", "rekey_period": "0", "send_sci": "true"}}

There is primary_cak, and there's no fallback_cak:
https://github.com/sonic-net/sonic-buildimage/blob/master/src/sonic-yang-models/yang-models/sonic-macsec.yang#L73

Steps to reproduce the issue:

1. Create virtual testbed kvmtest-t0-sonic
2. Run test macsec/test_deployment.py, check MACSEC_PROFILE table

Describe the results you received:

There is primary_cak, and there's no fallback_cak

Describe the results you expected:

MACSEC_PROFILE table should match yang definition

Output of show version:

(paste your output here)

Output of show techsupport:

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