i40e: fix setting user defined RSS hash key

Previously, when using ethtool to change the RSS hash key, ethtool would
report back saying the old key was still being used and no error was
reported.  It was unclear whether it was being reported incorrectly or
being set incorrectly.  Debugging revealed 'i40e_set_rxfh()' returned
zero immediately instead of setting the key because a user defined
indirection table is not supplied when changing the hash key.

This fix instead changes it such that if an indirection table is not
supplied, then a default one is created and the hash key is now
correctly set.

Change-ID: Iddb621897ecf208650272b7ee46702cad7b69a71
Signed-off-by: Alan Brady <alan.brady@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>