[Settings] Add per-netdevice settings block

Add a configuration settings block for each net device.  This will
provide the parent scope for settings applicable only to that network
device (e.g. non-volatile options stored on the NIC, options obtained via
DHCP, etc.).

Expose the MAC address as a setting.

src/include/gpxe/dhcp.h

@@ -177,6 +177,15 @@ struct job_interface;
  */
 #define DHCP_EB_SIADDR DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 3 )
 
+/** MAC address
+ *
+ * This option is used internally to contain the network device
+ * hardware address, in order to provide a consistent approach to
+ * storing and processing options.  It should never be present in a
+ * DHCP packet.
+ */
+#define DHCP_EB_MAC DHCP_ENCAP_OPT ( DHCP_EB_ENCAP, 4 )
+
 /*
  * Tags in the range 0x10-0x7f are reserved for feature markers
  *

src/include/gpxe/errfile.h

@@ -129,6 +129,7 @@
 #define ERRFILE_dns			( ERRFILE_NET | 0x00110000 )
 #define ERRFILE_tftp			( ERRFILE_NET | 0x00120000 )
 #define ERRFILE_infiniband		( ERRFILE_NET | 0x00130000 )
+#define ERRFILE_netdev_settings		( ERRFILE_NET | 0x00140000 )
 
 #define ERRFILE_image		      ( ERRFILE_IMAGE | 0x00000000 )
 #define ERRFILE_elf		      ( ERRFILE_IMAGE | 0x00010000 )

src/include/gpxe/netdevice.h

@@ -11,6 +11,7 @@
 #include <gpxe/list.h>
 #include <gpxe/tables.h>
 #include <gpxe/refcnt.h>
+#include <gpxe/settings.h>
 
 struct io_buffer;
 struct net_device;
@@ -243,6 +244,9 @@ struct net_device {
 	/** Device statistics */
 	struct net_device_stats stats;
 
+	/** Configuration settings applicable to this device */
+	struct settings settings;
+
 	/** Driver private data */
 	void *priv;
 };
@@ -360,6 +364,8 @@ extern int net_tx ( struct io_buffer *iobuf, struct net_device *netdev,
 extern int net_rx ( struct io_buffer *iobuf, struct net_device *netdev,
 		    uint16_t net_proto, const void *ll_source );
 
+extern struct settings_operations netdev_settings_operations;
+
 /**
  * Complete network transmission
  *

src/include/gpxe/settings.h

@@ -17,7 +17,7 @@ struct in_addr;
 
 /** Settings block operations */
 struct settings_operations {
-	/** Set value of setting
+	/** Store value of setting
 	 *
 	 * @v settings		Settings block
 	 * @v tag		Setting tag number