[cachedhcp] Automatically open network device matching cached DHCPACK

It is unintuitive to have to include an "ifopen" at the start of an
autoexec.ipxe script.  Provide a mechanism for upper-layer drivers to
mark a network device to be opened automatically upon registration,
and do so for the device to which the cached DHCPACK is applied.

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

src/core/cachedhcp.c

@@ -171,6 +171,9 @@ static int cachedhcp_apply ( struct cached_dhcp_packet *cache,
 		settings = netdev_settings ( netdev );
 		DBGC ( colour, "CACHEDHCP %s is for %s\n",
 		       cache->name, netdev->name );
+
+		/* Mark network device to be opened automatically */
+		netdev->state |= NETDEV_AUTO_OPEN;
 	}
 
 	/* Register settings */

src/include/ipxe/netdevice.h

@@ -461,6 +461,9 @@ struct net_device {
 /** Network device must be polled even when closed */
 #define NETDEV_INSOMNIAC 0x0040
 
+/** Network device should be opened automatically */
+#define NETDEV_AUTO_OPEN 0x0080
+
 /** Link-layer protocol table */
 #define LL_PROTOCOLS __table ( struct ll_protocol, "ll_protocols" )
 

src/net/netdevice.c

@@ -836,6 +836,10 @@ int register_netdev ( struct net_device *netdev ) {
 		}
 	}
 
+	/* Attempt to open device automatically, if applicable */
+	if ( netdev->state & NETDEV_AUTO_OPEN )
+		netdev_open ( netdev );
+
 	return 0;
 
  err_probe: