[dynui] Allow for duplicate shortcut keys

When searching for a shortcut key, search first from the currently
selected menu item and then from the start of the list.

This allows several ways for a shortcut key to be meaningfully used
multiple times within the same menu.  For example, two sections may
have the same shortcut key:

  item --key s --gap (S)ection 1
  item ...
  item ...
  item --key s --gap (S)ection 2
  item ...

With the above menu, repeated "s" keypresses would cycle through the
sections.

As another example, entries within different sections may have the
same shortcut keys.  For example:

  item --key d --gap (D)ebian
  item --key s debst Debian (s)table release
  item --key u debun Debian (u)nstable release
  item --key f --gap (F)edora
  item --key s fedst Fedora (s)table release
  item --key u fedun Fedora (u)nstable release

With the above menu, a shortcut key sequence such as "f", "s" can be
used to select an entry within a specific section, avoiding the need
to choose shortcut keys that are globally unique within the menu.

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

src/include/ipxe/dynui.h

@@ -59,7 +59,7 @@ extern struct dynamic_ui * find_dynui ( const char *name );
 extern struct dynamic_item * dynui_item ( struct dynamic_ui *dynui,
 					  unsigned int index );
 extern struct dynamic_item * dynui_shortcut ( struct dynamic_ui *dynui,
-					      int key );
+					      int key, unsigned int index );
 extern int show_menu ( struct dynamic_ui *dynui, unsigned long timeout,
 		       unsigned long retimeout, const char *select,
 		       struct dynamic_item **selected );