[netdevice] Add "ifname" setting

Expose the network interface name (e.g. "net0") as a setting.  This
allows a script to obtain the name of the most recently opened network
interface via ${netX/ifname}.

Signed-off-by: Andrew Widdersheim <amwiddersheim@gmail.com>
Modified-by: Michael Brown <mcb30@ipxe.org>
Signed-off-by: Michael Brown <mcb30@ipxe.org>

src/net/netdev_settings.c

 	.description = "Chip",
 	.type = &setting_type_string,
 };
+const struct setting ifname_setting __setting ( SETTING_NETDEV, ifname ) = {
+	.name = "ifname",
+	.description = "Interface name",
+	.type = &setting_type_string,
+};
 
 /**
  * Store MAC address setting
 	return strlen ( chip );
 }
 
+/**
+ * Fetch ifname setting
+ *
+ * @v netdev		Network device
+ * @v data		Buffer to fill with setting data
+ * @v len		Length of buffer
+ * @ret len		Length of setting data, or negative error
+ */
+static int netdev_fetch_ifname ( struct net_device *netdev, void *data,
+				 size_t len ) {
+	const char *ifname = netdev->name;
+
+	strncpy ( data, ifname, len );
+	return strlen ( ifname );
+}
+
 /** A network device setting operation */
 struct netdev_setting_operation {
 	/** Setting */
 	{ &busloc_setting, NULL, netdev_fetch_busloc },
 	{ &busid_setting, NULL, netdev_fetch_busid },
 	{ &chip_setting, NULL, netdev_fetch_chip },
+	{ &ifname_setting, NULL, netdev_fetch_ifname },
 };
 
 /**