manager: get unicast ip only when the config one is not

[xhebox]

What problem does this PR solve?

Issue Number: close #383

Problem Summary: when tiproxy listens on 127.0.0.1:2379, it also tries to report another unicast IP, e.g. 192.168.4.43. This does not make sense.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Notable changes

• Has configuration change
• Has HTTP API interfaces change
• Has tiproxyctl change
• Other user behavior changes

Release note

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None

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: djshow832

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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2023-10-20 06:18:14.878331201 +0000 UTC m=+1983492.465441349: ☑️ agreed by djshow832.