migration: fix dump-vmstate with modules

To work correctly -dump-vmstate and vmstate-static-checker.py need to
dump all the supported vmstates.

But as some devices can be modules, they are not loaded at startup and not
dumped. Fix that by loading all available modules before dumping the
machine vmstate.

Fixes: 7ab6e7fcce ("qdev: device module support")
Cc: kraxel@redhat.com
Signed-off-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20211116072840.132731-1-lvivier@redhat.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

softmmu/vl.c

@@ -3766,6 +3766,7 @@ void qemu_init(int argc, char **argv, char **envp)
 
     if (vmstate_dump_file) {
         /* dump and exit */
+        module_load_qom_all();
         dump_vmstate_json_to_file(vmstate_dump_file);
         exit(0);
     }