qemu-options: update to show preferred boolean syntax for -vnc

The preferred syntax is to use "foo=on|off", rather than a bare
"foo" or "nofoo".

The on|off syntax has been supported since -vnc switched to use
QemuOpts in commit 4db14629c38611061fc19ec6927405923de84f08

Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
Message-Id: <20210216191027.595031-7-berrange@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

qemu-options.hx

@@ -2123,13 +2123,13 @@ SRST
     Following the display value there may be one or more option flags
     separated by commas. Valid options are
 
-    ``reverse``
+    ``reverse=on|off``
         Connect to a listening VNC client via a "reverse" connection.
         The client is specified by the display. For reverse network
         connections (host:d,``reverse``), the d argument is a TCP port
         number, not a display number.
 
-    ``websocket``
+    ``websocket=on|off``
         Opens an additional TCP listening port dedicated to VNC
         Websocket connections. If a bare websocket option is given, the
         Websocket port is 5700+display. An alternative port can be
@@ -2143,7 +2143,7 @@ SRST
         runs in unencrypted mode. If TLS credentials are provided, the
         websocket connection requires encrypted client connections.
 
-    ``password``
+    ``password=on|off``
         Require that password based authentication is used for client
         connections.
 
@@ -2180,7 +2180,7 @@ SRST
         on the fly while the VNC server is active. If missing, it will
         default to denying access.
 
-    ``sasl``
+    ``sasl=on|off``
         Require that the client use SASL to authenticate with the VNC
         server. The exact choice of authentication method used is
         controlled from the system / user's SASL configuration file for
@@ -2203,7 +2203,7 @@ SRST
         fly while the VNC server is active. If missing, it will default
         to denying access.
 
-    ``acl``
+    ``acl=on|off``
         Legacy method for enabling authorization of clients against the
         x509 distinguished name and SASL username. It results in the
         creation of two ``authz-list`` objects with IDs of
@@ -2213,13 +2213,13 @@ SRST
         This option is deprecated and should no longer be used. The new
         ``sasl-authz`` and ``tls-authz`` options are a replacement.
 
-    ``lossy``
+    ``lossy=on|off``
         Enable lossy compression methods (gradient, JPEG, ...). If this
         option is set, VNC client may receive lossy framebuffer updates
         depending on its encoding settings. Enabling this option can
         save a lot of bandwidth at the expense of quality.
 
-    ``non-adaptive``
+    ``non-adaptive=on|off``
         Disable adaptive encodings. Adaptive encodings are enabled by
         default. An adaptive encoding will try to detect frequently
         updated screen regions, and send updates in these regions using
@@ -2254,7 +2254,7 @@ SRST
         must be omitted, otherwise is must be present and specify a
         valid audiodev.
 
-    ``power-control``
+    ``power-control=on|off``
         Permit the remote client to issue shutdown, reboot or reset power
         control requests.
 ERST