[nvo] Expose non-volatile options block name

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

src/core/nvo.c

 		goto err_load;
 
 	/* Register settings */
-	if ( ( rc = register_settings ( &nvo->settings, parent, "nvo" ) ) != 0 )
+	if ( ( rc = register_settings ( &nvo->settings, parent,
+					NVO_SETTINGS_NAME ) ) != 0 )
 		goto err_register;
 
 	DBGC ( nvo, "NVO %p registered\n", nvo );

src/include/ipxe/nvo.h

 	struct dhcp_options dhcpopts;
 };
 
+/** Name of non-volatile options settings block */
+#define NVO_SETTINGS_NAME "nvo"
+
 extern void nvo_init ( struct nvo_block *nvo, struct nvs_device *nvs,
 		       size_t address, size_t len,
 		       int ( * resize ) ( struct nvo_block *nvo, size_t len ),