monitor: Point to "help" command on syntax error

When a command fails due to incorrect syntax or input, suggest using
the "help" command to get more information about the command.  This
is only applicable for HMP.

Signed-off-by: Bandan Das <bsd@redhat.com>
Acked-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Markus Armbruster <armbru@redhat.com>

monitor.c

@@ -4069,6 +4069,8 @@ static void handle_hmp_command(Monitor *mon, const char *cmdline)
 
     qdict = monitor_parse_arguments(mon, &cmdline, cmd);
     if (!qdict) {
+        monitor_printf(mon, "Try \"help %s\" for more information\n",
+                       cmd->name);
         return;
     }