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: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>