Fix show macsec crash after deleting macsec ports

[darius-nexthop]

Why I did it

config macsec port del <port> removes the macsec field from the CONFIG_DB PORT entry immediately, while the APPL_DB MACSEC_PORT_TABLE entry is cleaned up asynchronously by macsecmgrd. If show macsec runs in that window (for example, while deleting several ports at once), MACsecPort.dump_str finds the APPL_DB entry but no macsec field in CONFIG_DB and crashes:

File ".../show/plugins/macsec.py", line 158, in dump_str
    self.meta["profile"] = self.cfgMeta["macsec"]
KeyError: 'macsec'

The error is transient and re-running show macsec after teardown completes succeeds.

fixes #28584

Work item tracking

• Microsoft ADO (number only):

How I did it

Switch to self.cfgMeta.get("macsec", "") in MACsecPort.dump_str

If a port is mid-teardown, it will be shown with an empty profile instead of crashing, e.g.:

MACsec port(Ethernet5)
cipher_suite           GCM-AES-256
enable                 true
enable_encrypt         true
enable_protect         true
enable_replay_protect  false
profile
replay_window          0
send_sci               true

Reasoning is that the port still exists in APPL_DB, so we should still show the port in show macsec while it is still programmed. This output is transient and the port will simply disappear once macsecmgrd has unprogrammed it.

Also adds a guard for the port append in create_macsec_objs against None result from create_macsec_obj.

How to verify it

New regression test test_show_port_deleted_from_config: Ethernet5 in the mock DBs has an APPL_DB MACSEC_PORT_TABLE entry but no macsec field in CONFIG_DB (the mid-teardown state). Without the fix, test_show_all and the new test both crash with the KeyError above; with the fix the port shows with an empty profile and all macsec cli-plugin-tests pass.

Which release branch to backport (provide reason below if selected)

• 202305
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• 202608

Tracking issue/work item for backport/cherry-pick request (GitHub issue or Microsoft ADO): #28584
Failure type: day-one issue

Tested branch

• master
• 202305
• 202311
• 202405
• 202411
• 202505
• 202511
• 202512
• 202605
• 202608
• N/A

Test result

(with fix)
202511:

  MACsec port(Ethernet16)
  ------------  -----------
  cipher_suite  GCM-AES-256
  enable        true
  profile
  ------------  -----------

Description for the changelog

Fix show macsec KeyError crash when run while MACsec port deletion is still being processed.

Link to config_db schema for YANG module changes

N/A

A picture of a cute animal (not mandatory but encouraged)

[mssonicbld]

/azp run Azure.sonic-buildimage

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[mssonicbld]

This PR has backport request for branch(es): 202511.
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[mssonicbld]

This PR has backport request label(s) for branch(es): 202511, but is missing required test information. Please make sure you tick the tested branch(es) in the Tested branch section and provide test evidence (e.g., 202511: <test result>) in the Test result section as well in your PR description.

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[darius-nexthop]

/azp run Azure.sonic-buildimage

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[mssonicbld]

/azp run Azure.sonic-buildimage

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[mssonicbld]

This PR has backport request for branch(es): 202511,202605.

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[mssonicbld]

The Tested branch section has been ticked and Test result is provided for branch(es): 202511. Added label(s): Tested for 202511 Branch.

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[mssonicbld]

This PR has backport request label(s) for branch(es): 202605, but is missing required test information. Please make sure you tick the tested branch(es) in the Tested branch section and provide test evidence (e.g., 202605: <test result>) in the Test result section as well in your PR description.

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