USB: qcserial: Enable Diagnostics Monitor and GPS ports on Gobi 2000

this patch to qcserial.c enables the Diagnostics Monitor
and NMEA GPS ports on Qualcomm Gobi 2000 devices.

A Gobi 2000 device will provide 3 serial ports:
        # /dev/ttyUSB0 -> Diagnostics
        # /dev/ttyUSB1 -> 3G Modem
        # /dev/ttyUSB2 -> NMEA GPS port

* The Diagnostics Monitor uses Qualcomm's DM protocol; I used
  libqcdm (ModemManager) to talk to it, found it working, but at
  least DM commands 12 and 64 are not implemented on my device
  (Gobi 2000 built into Thinkpad x100e).

* Functionality of the 3G Modem port remains unchanged.

* The GPS port and how to enable it has been confirmed now in the
  Gobi 3000 source code at:
	https://www.codeaurora.org/patches/quic/gobi/
  Enable/disable GPS via:
        echo "\$GPS_START" > /dev/ttyUSB2
        # use GPS
        echo "\$GPS_STOP"  > /dev/ttyUSB2
Signed-off-by: NMatthias G. Eckermann <mge@arcor.de>

drivers/usb/serial/qcserial.c

@@ -152,7 +152,22 @@ static int qcprobe(struct usb_serial *serial, const struct usb_device_id *id)
 	case 3:
 	case 4:
 		/* Composite mode */
-		if (ifnum == 2) {
+		/* ifnum == 0 is a broadband network adapter */
+		if (ifnum == 1) {
+			/*
+			 * Diagnostics Monitor (serial line 9600 8N1)
+			 * Qualcomm DM protocol
+			 * use "libqcdm" (ModemManager) for communication
+			 */
+			dbg("Diagnostics Monitor found");
+			retval = usb_set_interface(serial->dev, ifnum, 0);
+			if (retval < 0) {
+				dev_err(&serial->dev->dev,
+					"Could not set interface, error %d\n",
+					retval);
+				retval = -ENODEV;
+			}
+		} else if (ifnum == 2) {
 			dbg("Modem port found");
 			retval = usb_set_interface(serial->dev, ifnum, 0);
 			if (retval < 0) {
@@ -163,6 +178,20 @@ static int qcprobe(struct usb_serial *serial, const struct usb_device_id *id)
 				kfree(data);
 			}
 			return retval;
+		} else if (ifnum==3) {
+			/*
+			 * NMEA (serial line 9600 8N1)
+			 * # echo "\$GPS_START" > /dev/ttyUSBx
+			 * # echo "\$GPS_STOP"  > /dev/ttyUSBx
+			 */
+			dbg("NMEA GPS interface found");
+			retval = usb_set_interface(serial->dev, ifnum, 0);
+			if (retval < 0) {
+				dev_err(&serial->dev->dev,
+					"Could not set interface, error %d\n",
+					retval);
+				retval = -ENODEV;
+			}
 		}
 		break;