SPINEL_PROP_UART_BITRATE value

UART Bitrate Format: `L` If the NCP is using a UART to communicate with the host, this property allows the host to change the bitrate of the serial connection. The value encoding is `L`, which is a little-endian 32-bit unsigned integer. The host should not assume that all possible numeric values are supported. If implemented by the NCP, this property should be persistent across software resets and forgotten upon hardware resets. This property is only implemented when a UART is being used for Spinel. This property is optional. When changing the bitrate, all frames will be received at the previous bitrate until the response frame to this command is received. Once a successful response frame is received by the host, all further frames will be transmitted at the new bitrate.