[sanboot] Add "sanhook" and "sanunhook" commands

Expose the multiple-SAN-drive capability of the iPXE core via the iPXE
command line by adding commands to hook and unhook additional drives.

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

src/usr/pxemenu.c

@@ -377,7 +377,7 @@ int pxe_menu_boot ( struct net_device *netdev ) {
 		return -ENOMEM;
 
 	/* Attempt boot */
-	rc = uriboot ( uri, NULL );
+	rc = uriboot ( uri, NULL, 0, URIBOOT_NO_SAN );
 	uri_put ( uri );
 	return rc;
 }