fix: Correct type for conference offline peer numbers.

[iphydf]

Also return count as uint32_t, not as peer number.

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This change is 

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (0627c36) 73.05% compared to head (be82a3e) 73.10%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #2704 +/- ## ========================================== + Coverage 73.05% 73.10% +0.04% ========================================== Files 149 149 Lines 30517 30517 ========================================== + Hits 22294 22309 +15 + Misses 8223 8208 -15 ```

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