Bluetooth LE Connection Priority test refactor

Use the new callback to verify that the connection interval was changed.

Change connection parameters three times, and expect that the connection
interval value descends on both the client and the server.

Bug: 139829044
Test: refactored Bluetooth LE CTS test
Change-Id: Iff5ac5dfdac4991d018ce78315d9f32bc4a0e8b9
5 files changed