rootless: fix proxying UDP packets

UDP reply packets were not proxied: https://github.com/rootless-containers/rootlesskit/issues/86

The issue was fixed in RootlessKit v0.7.1: https://github.com/rootless-containers/rootlesskit/pull/87

Full changes since v0.7.0: https://github.com/rootless-containers/rootlesskit/compare/v0.7.0...v0.7.1

Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>
(cherry picked from commit 658723badd2fe2db6aacfddec17d78df2997a905)
Signed-off-by: Akihiro Suda <akihiro.suda.cz@hco.ntt.co.jp>

hack/dockerfile/install/rootlesskit.installer

@@ -1,7 +1,7 @@
 #!/bin/sh
 
-# v0.7.0
-ROOTLESSKIT_COMMIT=791ac8cb209a107505cd1ca5ddf23a49913e176c
+# v0.7.1
+: ${ROOTLESSKIT_COMMIT:=76c4e26750da3986fa0e741464fbf0fcd55bea71}
 
 install_rootlesskit() {
 	case "$1" in