USB: Change acm_iad_descriptor bFunctionProtocol to USB_CDC_ACM_PROTO_AT_V25TER
The protocol code is set 00 in IAD and it's set to 01 in ACM control
interface descriptor in f_acm.c file. Due to this, windows is unable to
install the modem(ACM) driver based on class-subclass-protocol matching.
This patch corrects the protocol code in ACM IAD to the same as in
acm_control_interface_desc protocol code.