ila: Fix rhashtable walker list corruption

ila_xlat_nl_cmd_flush uses rhashtable walkers allocated from the
stack but it never frees them.  This corrupts the walker list of
the hash table.

This patch fixes it.

Reported-by: syzbot+dae72a112334aa65a159@syzkaller.appspotmail.com
Fixes: b6e71bde ("ila: Flush netlink command to clear xlat...")
Signed-off-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/ila/ila_xlat.c

@@ -417,6 +417,7 @@ int ila_xlat_nl_cmd_flush(struct sk_buff *skb, struct genl_info *info)
 
 done:
 	rhashtable_walk_stop(&iter);
+	rhashtable_walk_exit(&iter);
 	return ret;
 }