libxl: initialize shutdown inhibit callback

The libxl driver already tries to call shutdown inhibit callback in the
right places, but only if it's set. That last part was missing,
resulting in premature shutdown when running libvirtd
--timeout=...
Signed-off-by: NMarek Marczykowski-Górecki <marmarek@invisiblethingslab.com>
Reviewed-by: NJim Fehlig <jfehlig@suse.com>

src/libxl/libxl_driver.c

@@ -648,8 +648,8 @@ libxlAddDom0(libxlDriverPrivatePtr driver)
 
 static int
 libxlStateInitialize(bool privileged,
-                     virStateInhibitCallback callback G_GNUC_UNUSED,
-                     void *opaque G_GNUC_UNUSED)
+                     virStateInhibitCallback callback,
+                     void *opaque)
 {
     libxlDriverConfigPtr cfg;
     char *driverConf = NULL;
@@ -670,6 +670,9 @@ libxlStateInitialize(bool privileged,
         return VIR_DRV_STATE_INIT_ERROR;
     }
 
+    libxl_driver->inhibitCallback = callback;
+    libxl_driver->inhibitOpaque = opaque;
+
     /* Allocate bitmap for vnc port reservation */
     if (!(libxl_driver->reservedGraphicsPorts =
           virPortAllocatorRangeNew(_("VNC"),