when recv is processed, the _recv_buf.valid must be cleared

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
change some code, may be useless

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
fix some code, for exp crc16 is wrong fix it

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

Signed-off-by: kevinhuhui <huhuikevin@gmail.com>
change the crc16 to tool.c

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