Function readStreamRaw

See

https://datatracker.ietf.org/doc/html/draft-rquattle-spinel-unified#section-5.6.2.1

Assumes payload comes from spinel.payload and offset is right after SpinelPropertyId.STREAM_RAW, per below

Packed-Encoding: "dD"

+---------+----------------+------------+----------------+ | Octets: | 2 | n | n | +---------+----------------+------------+----------------+ | Fields: | FRAME_DATA_LEN | FRAME_DATA | FRAME_METADATA | +---------+----------------+------------+----------------+

from pyspinel (https://github.com/openthread/pyspinel/blob/main/sniffer.py#L283): metadata format (totally 19 bytes or 26 bytes): 0. RSSI(int8)

1. Noise Floor(int8)
2. Flags(uint16)
3. PHY-specific data struct contains: 3.0 Channel(uint8) 3.1 LQI(uint8) 3.2 Timestamp in microseconds(uint64)
4. Vendor data struct contains: 4.0 Receive error(uint8)
5. (optional) MAC data struct contains: 5.0 ACK key ID(uint8) 5.1 ACK frame counter(uint32)