USB: serial: add generic get_icount implementation

Add generic get_icount implementation that subdrivers relying on the
port interrupt counters can use.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
index 47c8d2c..c786ee7 100644
--- a/include/linux/usb/serial.h
+++ b/include/linux/usb/serial.h
@@ -335,6 +335,8 @@
 extern void usb_serial_generic_unthrottle(struct tty_struct *tty);
 extern int usb_serial_generic_tiocmiwait(struct tty_struct *tty,
 							unsigned long arg);
+extern int usb_serial_generic_get_icount(struct tty_struct *tty,
+					struct serial_icounter_struct *icount);
 extern int usb_serial_generic_register(void);
 extern void usb_serial_generic_deregister(void);
 extern int usb_serial_generic_submit_read_urbs(struct usb_serial_port *port,