ui/qmp-cmds: Improve two error messages

set_password with "protocol": "vnc" supports only "connected": "keep".
Any other value is rejected with

    Invalid parameter 'connected'

Improve this to

    parameter 'connected' must be 'keep' when 'protocol' is 'vnc'

client_migrate_info requires "port" or "tls-port".  When both are
missing, it fails with

    Parameter 'port/tls-port' is missing

Improve this to

    parameter 'port' or 'tls-port' is required

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Message-ID: <20231031111059.3407803-5-armbru@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>

ui/ui-qmp-cmds.c

@@ -44,7 +44,8 @@ void qmp_set_password(SetPasswordOptions *opts, Error **errp)
         assert(opts->protocol == DISPLAY_PROTOCOL_VNC);
         if (opts->connected != SET_PASSWORD_ACTION_KEEP) {
             /* vnc supports "connected=keep" only */
-            error_setg(errp, QERR_INVALID_PARAMETER, "connected");
+            error_setg(errp, "parameter 'connected' must be 'keep'"
+                       " when 'protocol' is 'vnc'");
             return;
         }
         /*
@@ -195,7 +196,7 @@ void qmp_client_migrate_info(const char *protocol, const char *hostname,
         }
 
         if (!has_port && !has_tls_port) {
-            error_setg(errp, QERR_MISSING_PARAMETER, "port/tls-port");
+            error_setg(errp, "parameter 'port' or 'tls-port' is required");
             return;
         }