Only allow a single BLE request at once

[maikeriva]

While debugging the application with a custom provisioner firmware code, I noticed it may occasionally send a second request via BLE while still waiting for the previous one's response. When that happens, the response listener gets overwritten (or null'ed) and the response will just went by unprocessed.

The fix which worked for me was to set the semaphore token number to 0 and ensure that the listener is accessed only within the semaphore's protection.

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