libxl: do not try to redo incoming migration on reboot of migrated domain

After a migration, reboot was trying to receive another incoming
migration, instead of restarting the domain it already has.

Signed-off-by: Ian Jackson <ian.jackson@eu.citrix.com>
Tested-by: Andreas Olsowski <andreas.olsowski@leuphana.de>
Committed-by: Ian Jackson <ian.jackson@eu.citrix.com>

tools/libxl/xl_cmdimpl.c

@@ -1516,6 +1516,11 @@ start:
         ret = libxl_domain_create_restore(ctx, &d_config,
                                             cb, &child_console_pid,
                                             &domid, restore_fd);
+        /*
+         * On subsequent reboot etc we should create the domain, not
+         * restore/migrate-receive it again.
+         */
+        restore_file = NULL;
     }else{
         ret = libxl_domain_create_new(ctx, &d_config,
                                         cb, &child_console_pid, &domid);