ipipe: Activate IRQ in ipipe_enable_irq

Likely needed since c942cee4 which split enabling and startup.

This fixes unpopulated vectors in the IOAPIC on x86 at least, possibly
more.
Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>

kernel/irq/chip.c

@@ -1093,6 +1093,7 @@ int ipipe_enable_irq(unsigned int irq)
 	struct irq_desc *desc;
 	struct irq_chip *chip;
 	unsigned long flags;
+	int err;
 
 	desc = irq_to_desc(irq);
 	if (desc == NULL)
@@ -1104,6 +1105,10 @@ int ipipe_enable_irq(unsigned int irq)
 
 		ipipe_root_only();
 
+		err = irq_activate(desc);
+		if (err)
+			return err;
+
 		raw_spin_lock_irqsave(&desc->lock, flags);
 		if (desc->istate & IPIPE_IRQS_NEEDS_STARTUP) {
 			desc->istate &= ~IPIPE_IRQS_NEEDS_STARTUP;