restore: load ip6tables modules on restore as well

The restore process uses these modules as well, so let's modprobe them.
This prevents:

(00.217856)      1:     Running ip rule delete
(00.218970)      1:     Running ip rule delete
(00.220059)      1:     Running ip rule delete
(00.221695)      1:     Running ip rule restore
(00.223068)      1:     Running iptables-restore for iptables-restore
(00.439385)      1:     Running ip6tables-restore for ip6tables-restore
modprobe: ERROR: could not insert 'ip6_tables': Operation not permitted
ip6tables-restore v1.6.0: ip6tables-restore: unable to initialize table 'filter'

Error occurred at line: 2
Try `ip6tables-restore -h' or 'ip6tables-restore --help' for more information.
Signed-off-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>

criu/crtools.c

@@ -659,6 +659,7 @@ int main(int argc, char *argv[], char *envp[])
 	}
 
 	if (!strcmp(argv[optind], "restore")) {
+		preload_netfilter_modules();
 		if (tree_id)
 			pr_warn("Using -t with criu restore is obsoleted\n");