x86, xen: do multicall callbacks with interrupts disabled

We can't call the callbacks after enabling interrupts, as we may get a
nested multicall call, which would cause a great deal of havok.

Signed-off-by: Jeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

arch/x86/xen/multicalls.c

@@ -170,15 +170,15 @@ void xen_mc_flush(void)
 	} else
 		BUG_ON(b->argidx != 0);
 
-	local_irq_restore(flags);
-
 	for (i = 0; i < b->cbidx; i++) {
 		struct callback *cb = &b->callbacks[i];
 
 		(*cb->fn)(cb->data);
 	}
 	b->cbidx = 0;
 
+	local_irq_restore(flags);
+
 	WARN_ON(ret);
 }