CP-17631: Don't use a default QEMU keymap

Until now we have been defaulting the keymap to `en-us` but this
prevents VNC clients from using the QEMU ExtendedKeyEvent extension for
passing raw scan codes.

If a keymap is not passed to QEMU, it will default to using `en-us`
anyway but will enable the ExtendedKeyEvent extension.

This does not change the behaviour for when a keymap has actually been
specified. In this case, it is still honoured and passed to QEMU with
the `-k` option.

Signed-off-by: Si Beaumont <simon.beaumont@citrix.com>

Author: simonjbeaumont

xc/device.ml

@@ -1418,7 +1418,7 @@ type disp_intf_opt =
 (* Display output / keyboard input *)
 type disp_opt =
 	| NONE
-	| VNC of disp_intf_opt * string option * bool * int * string (* IP address, auto-allocate, port if previous false, keymap *)
+	| VNC of disp_intf_opt * string option * bool * int * string option (* IP address, auto-allocate, port if previous false, keymap *)
 	| SDL of disp_intf_opt * string (* X11 display *)
 
 type media = Disk | Cdrom
@@ -1551,7 +1551,7 @@ let cmdline_of_disp info =
 			let ip_addr = Opt.default "127.0.0.1" ip_addr_opt
 			and port = if auto then "1" else string_of_int port in
 			["-vnc"; ip_addr ^ ":" ^ port] in
-		let keymap_opt = ["-k"; keymap] in
+		let keymap_opt = match keymap with Some k -> ["-k"; k] | None -> [] in
 		List.flatten [unused_opt; vnc_opt; keymap_opt]
 	in
 	let disp_options, wait_for_port =

xc/device.mli

@@ -178,7 +178,7 @@ sig
 
 	type disp_opt =
 		| NONE
-		| VNC of disp_intf_opt * string option * bool * int * string (* IP address, auto-allocate, port if previous false, keymap *)
+		| VNC of disp_intf_opt * string option * bool * int * string option (* IP address, auto-allocate, port if previous false, keymap *)
 		| SDL of disp_intf_opt * string (* X11 display *)
 
 	type media = Disk | Cdrom

xc/xenops_server_xen.ml

@@ -1102,7 +1102,7 @@ module VM = struct
 					?(nics=[]) ?(disks=[]) ?(vgpus=[])
 					?(pci_emulations=[]) ?(usb=Device.Dm.Disabled)
 					?(parallel=None)
-					?(acpi=true) ?(video=Cirrus) ?(keymap="en-us")
+					?(acpi=true) ?(video=Cirrus) ?keymap
 					?vnc_ip ?(pci_passthrough=false) ?(hvm=true) ?(video_mib=4) () =
 				let video = match video, vgpus with
 					| Cirrus, [] -> Device.Dm.Cirrus