Fix incorrect parsing of Out-Of-Band data

[dordnung]

Inputting Out-Of-Band data will never be possible, as the input is not parsed as hex string put every char in the hex string will be converted to its ascii representation thus also only considering the first 8 bytes.

There are some reports considering this issue:
https://devzone.nordicsemi.com/f/nordic-q-a/47932/oob-works-with-mcp-but-fails-with-nrf-connect
https://devzone.nordicsemi.com/f/nordic-q-a/16693/error-oob-static-key-nrf-connect

This pull request will fix this by converting every hex byte in the hex string as byte.

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✅ dordnung
❌ David Ordnung

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