RF can work at 250Kbps or 1M bps

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
add a function to read rssi value

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
fix a plc_mac bug, if _recv_buf.valid not zero, we must
clear it

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
add hw2000 rf send test, recv test can recv data from plc and rf

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>