[le audio] Update mBroadcastDescriptors before notifying by callbacks

Broadcast application might rely on getAllBroadcastMetadata() to check the active broadcasts.
There would be race conditions that we're notifying the clients before updating the mBroadcastDescriptors for getAllBroadcastMetadata().
We should notify by callbacks after updating the metadata.

This change only applied to le audio broadcast feature.
no-op, only sequence change.

Bug: 317395992
Bug: 316005152
Test: atest LeAudioServiceTest
Test: manual test with le audio broadcast audio sharing to confirm
start/stop broadcast has no issue

Change-Id: I6e6357facd64a1d688a3a43b0004ef69f883ff20