print_ht in rhashtable_test calls rht_dereference() with neither
RCU protection or the mutex.  This triggers an RCU warning.
So take the mutex to silence the warning.
Acked-by: NHerbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: NNeilBrown <neilb@suse.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>