xen: modify xenstore watch event interface

Today a Xenstore watch event is delivered via a callback function
declared as:

void (*callback)(struct xenbus_watch *,
                 const char **vec, unsigned int len);

As all watch events only ever come with two parameters (path and token)
changing the prototype to:

void (*callback)(struct xenbus_watch *,
                 const char *path, const char *token);

is the natural thing to do.

Apply this change and adapt all users.

Cc: konrad.wilk@oracle.com
Cc: roger.pau@citrix.com
Cc: wei.liu2@citrix.com
Cc: paul.durrant@citrix.com
Cc: netdev@vger.kernel.org

Signed-off-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Paul Durrant <paul.durrant@citrix.com>
Reviewed-by: Wei Liu <wei.liu2@citrix.com>
Reviewed-by: Roger Pau Monné <roger.pau@citrix.com>
Reviewed-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Signed-off-by: Boris Ostrovsky <boris.ostrovsky@oracle.com>
diff --git a/drivers/xen/xen-pciback/xenbus.c b/drivers/xen/xen-pciback/xenbus.c
index 3f0aee0..3814b44 100644
--- a/drivers/xen/xen-pciback/xenbus.c
+++ b/drivers/xen/xen-pciback/xenbus.c
@@ -652,7 +652,7 @@ static int xen_pcibk_setup_backend(struct xen_pcibk_device *pdev)
 }
 
 static void xen_pcibk_be_watch(struct xenbus_watch *watch,
-			     const char **vec, unsigned int len)
+			       const char *path, const char *token)
 {
 	struct xen_pcibk_device *pdev =
 	    container_of(watch, struct xen_pcibk_device, be_watch);