USB: serial: export generic throttle and unthrottle

Allow drivers to use the generic throttle and unthrottle implementation.
This makes sense for drivers using the generic read functionality.

Note that drivers need to set these explicitly in order to enable them
(i.e., we do not set them at port probe if not defined).
Signed-off-by: NJohan Hovold <jhovold@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@suse.de>

drivers/usb/serial/generic.c

@@ -517,6 +517,7 @@ void usb_serial_generic_throttle(struct tty_struct *tty)
 	port->throttle_req = 1;
 	spin_unlock_irqrestore(&port->lock, flags);
 }
+EXPORT_SYMBOL_GPL(usb_serial_generic_throttle);
 
 void usb_serial_generic_unthrottle(struct tty_struct *tty)
 {
@@ -534,6 +535,7 @@ void usb_serial_generic_unthrottle(struct tty_struct *tty)
 	if (was_throttled)
 		usb_serial_generic_submit_read_urb(port, GFP_KERNEL);
 }
+EXPORT_SYMBOL_GPL(usb_serial_generic_unthrottle);
 
 #ifdef CONFIG_MAGIC_SYSRQ
 int usb_serial_handle_sysrq_char(struct tty_struct *tty,