fix cond_unlock for keys that do not fit in a single unlock message

[danielhrisca]

The UNLOCK commands must contain the remaining length of the key bytes.

MAX_CTO = 8 bytes (CAN)
TotalLengthOf(seed) = 19 bytes
TotalLengthOf(key) = 10 bytes
Seed = 99 88 77 66 55 44 33 22 11 00 11 22 33 44 55 66 77 88 99
Key = 98 76 54 32 10 01 23 45 67 89

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)
• [ ] I have read the CONTRIBUTING document.
• [ ] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.