ot::Ncp::NcpBase::IidToInstance() method

Returns an OT instance for the given IID Returns an OpenThread instance object associated to the given IID. If multipan interface is not enabled or build is not for RCP returned value is the same instance object regardless of the aIid parameter In current implementation nullptr is returned for broadcast IID and values exceeding the instances count but lower than kSpinelInterfaceCount.