[netdevice] Allow network devices to disclaim IRQ support at runtime

VLAN and 802.11 devices use a network device operations structure that
wraps an underlying structure.  For example, the vlan_operations
structure wraps the network device operations structure of the
underlying trunk device.  This can cause false positives from the
current implementation of netdev_irq_supported(), which will always
report that VLAN devices support interrupts since it has no visibility
into the support provided by the underlying trunk device.

Fix by allowing network devices to explicitly flag that interrupts are
not supported, despite the presence of an irq() method.

Originally-fixed-by: Wissam Shoukair <wissams@mellanox.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/include/ipxe/netdevice.h

 /** Network device receive queue processing is frozen */
 #define NETDEV_RX_FROZEN 0x0004
 
+/** Network device interrupts are unsupported
+ *
+ * This flag can be used by a network device to indicate that
+ * interrupts are not supported despite the presence of an irq()
+ * method.
+ */
+#define NETDEV_IRQ_UNSUPPORTED 0x0008
+
 /** Link-layer protocol table */
 #define LL_PROTOCOLS __table ( struct ll_protocol, "ll_protocols" )
 
  */
 static inline __attribute__ (( always_inline )) int
 netdev_irq_supported ( struct net_device *netdev ) {
-	return ( netdev->op->irq != NULL );
+	return ( ( netdev->op->irq != NULL ) &&
+		 ! ( netdev->state & NETDEV_IRQ_UNSUPPORTED ) );
 }
 
 /**

src/net/80211/net80211.c

 		 NET80211_MAX_CHANNELS * sizeof ( dev->channels[0] ) );
 	dev->channel = 0;
 
+	/* Mark device as not supporting interrupts, if applicable */
+	if ( ! ops->irq )
+		dev->netdev->state |= NETDEV_IRQ_UNSUPPORTED;
+
 	list_add_tail ( &dev->list, &net80211_devices );
 	return register_netdev ( dev->netdev );
 }

src/net/vlan.c

 	snprintf ( netdev->name, sizeof ( netdev->name ), "%s-%d",
 		   trunk->name, vlan->tag );
 
+	/* Mark device as not supporting interrupts, if applicable */
+	if ( ! netdev_irq_supported ( trunk ) )
+		netdev->state |= NETDEV_IRQ_UNSUPPORTED;
+
 	/* Register VLAN device */
 	if ( ( rc = register_netdev ( netdev ) ) != 0 ) {
 		DBGC ( netdev, "VLAN %s could not register: %s\n",