amt: remove duplicate include in amt.c

'net/protocol.h' included in 'drivers/net/amt.c' is duplicated.

Reported-by: Zeal Robot <zealci@zte.com.cn>
Signed-off-by: Zhang Mingyu <zhang.mingyu@zte.com.cn>
Signed-off-by: David S. Miller <davem@davemloft.net>