ixgbe: Refactor the RSS configuration code

This patch is a preparation for enablement of ethtool RSS indirection
table and hash key querying. We don't want to read registers every time
the RSS info is queried. Therefore we will store its current content in the
arrays in the adapter struct and will read it from there (instead of from
registers) when requested.

Will change the code that writes the indirection table and hash key into
the HW registers to take its content from these arrays. This will also
simplify the indirection table updating ethtool callback implementation
in the future.

Signed-off-by: Vlad Zolotarov <vladz@cloudius-systems.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>