Small update to SYS_IRQCTL -> setting an interrupt policy now allows the caller

to provide an index (0 .. 31) that is passed in the HARD_INT message when an
interrupt occurs. The NOTIFY_ARG field contains a bitmap with all indexes for
which an interrupt occured.

drivers/printer/printer.c

@@ -340,6 +340,7 @@ PRIVATE void do_initialize()
   tickdelay(1);			/* easily satisfies Centronics minimum */
   				/* was 2 millisecs; now is ~17 millisecs */
   sys_outb(port_base + 2, PR_SELECT);
+  irq_hook_id = 0;
   sys_irqsetpolicy(PRINTER_IRQ, 0, &irq_hook_id);
   sys_irqenable(&irq_hook_id);