SPINEL_PROP_STREAM_LOG value

Log Stream Format: `UD` (stream, read only) This property is a read-only streaming property which provides formatted log string from NCP. This property provides asynchronous `CMD_PROP_VALUE_IS` updates with a new log string and includes optional meta data. `U`: The log string `D`: Log metadata (optional). Any data after the log string is considered metadata and is OPTIONAL. Presence of `SPINEL_CAP_OPENTHREAD_LOG_METADATA` capability indicates that OpenThread log metadata format is used as defined below: `C`: Log level (as per definition in enumeration `SPINEL_NCP_LOG_LEVEL_`) `i`: OpenThread Log region (as per definition in enumeration `SPINEL_NCP_LOG_REGION_). `X`: Log timestamp = +