fib_trie: leaf_walk_rcu should not compute key if key is less than pn->key

fib_trie: leaf_walk_rcu should not compute key if key is less than pn->key

Orabug: 22623836

[ Upstream commit c2229fe1430d4e1c70e36520229dd64a87802b20 ]

We were computing the child index in cases where the key value we were
looking for was actually less than the base key of the tnode.  As a result
we were getting incorrect index values that would cause us to skip over
some children.

To fix this I have added a test that will force us to use child index 0 if
the key we are looking for is less than the key of the current tnode.

Fixes: 8be33e955cb9 ("fib_trie: Fib walk rcu should take a tnode and key instead of a trie and a leaf")
Reported-by: Brian Rak <brak@gameservers.com>
Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
(cherry picked from commit a8cf2fa6a557924d9d3d3ed67bd4afeeac37b91b)
Signed-off-by: Dan Duval <dan.duval@oracle.com>