[border-agent] use new otBorderAgent ephemeral key APIs (#2674)
#665
| Job | Run time |
|---|---|
| 24m 12s | |
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| 20m 12s | |
| 24m 5s | |
| 51s | |
| 23m 50s | |
| 20m 15s | |
| 1m 21s | |
| 24m 2s | |
| 5m 1s | |
| 6m 50s | |
| 2h 34m 52s |