eth: e1000e: migrate to new RXFH callbacks

eth: e1000e: migrate to new RXFH callbacks

Migrate to new callbacks added by commit 9bb00786fc61 ("net: ethtool:
add dedicated callbacks for getting and setting rxfh fields").
This driver's RXFH config is read only / fixed and it's the only
get_rxnfc sub-command the driver supports. So convert the get_rxnfc
handler into a get_rxfh_fields handler.

Reviewed-by: Joe Damato <joe@dama.to>
Reviewed-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Link: https://patch.msgid.link/20250614180638.4166766-5-kuba@kernel.org
Signed-off-by: Jakub Kicinski <kuba@kernel.org>