[infiniband] Indicate that device does not support interrupts

Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/drivers/net/ipoib.c

 	ib_poll_eq ( ibdev );
 }
 
-/**
- * Enable/disable interrupts on IPoIB network device
- *
- * @v netdev		Network device
- * @v enable		Interrupts should be enabled
- */
-static void ipoib_irq ( struct net_device *netdev __unused,
-			int enable __unused ) {
-	/* No implementation */
-}
-
 /**
  * Handle IPv4 broadcast multicast group join completion
  *
 	.close		= ipoib_close,
 	.transmit	= ipoib_transmit,
 	.poll		= ipoib_poll,
-	.irq		= ipoib_irq,
 };
 
 /**