This commit introduces new Spinel properties to support CLI service in
NCP.
* Added `SPINEL_PROP_STREAM_CLI` property: This streaming property
provides a bidirectional channel for interacting with the NCP's
command-line interface (CLI). The host can send CLI commands to the
NCP by setting this property. The NCP will then execute the
commands. The NCP will send the output of the executed command (if
any) back to the host via unsolicited notifications of this same
property.
Yang Song