test_rhashtable: add test case for rhltable with duplicate objects

test_rhashtable: add test case for rhltable with duplicate objects

BugLink: http://bugs.launchpad.net/bugs/1760585
[ Upstream commit 499ac3b60f657dae82055fc81c7b01e6242ac9bc ]

Tries to insert duplicates in the middle of bucket's chain:
bucket 1:  [[val 21 (tid=1)]] -> [[ val 1 (tid=2),  val 1 (tid=0) ]]

Reuses tid to distinguish the elements insertion order.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Acked-by: Herbert Xu <herbert@gondor.apana.org.au>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>