ice: update the number of available RSS queues

It was possible to have Rx queues that were not available for use
by RSS. This would happen when increasing the number of Rx queues
while there was a user defined RSS LUT.

Always update the number of available RSS queues when changing the
number of Rx queues.

Fixes: 87324e74 ("ice: Implement ethtool ops for channels")
Signed-off-by: Henry Tieman <henry.w.tieman@intel.com>
Tested-by: Tony Brelinski <tonyx.brelinski@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>