dm/scheduler: fix inconsistent of relay status (#3474)

[ti-chi-bot]

This is an automated cherry-pick of #3474

What problem does this PR solve?

close #3478

What is changed and how it works?

when receive keepalive, get relay source from correct place

Check List

Tests

• Integration test

Code changes

Side effects

Related changes

• need cherry-pick to release

Release note

 Fix a bug that when master and worker restart in a particular order, relay status in DM-master is wrong

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[lichunzhu]

need to resolve the conflicts first

[lance6716]

waiting #3944

[lance6716]

/run-all-tests

[lance6716]

replaced by #4009