Function parse_lock_slot 

pub fn parse_lock_slot(payload: &[u8]) -> Result<u8, PayloadError>

Parse the payload of CommandOpcode::LockSlot.

Layout: magic (4) || slot (1).

Errors

• PayloadError::WrongLen if the payload is not exactly 5 bytes.
• PayloadError::MagicMismatch if the first 4 bytes are not LOCK_SLOT_MAGIC.