eth: fbnic: migrate to new RXFH callbacks

Add support for the new rxfh_fields callbacks, instead of de-muxing
the rxnfc calls. The code is moved as we try to declare the functions
in the order ing which they appear in the ops struct.

Link: https://patch.msgid.link/20250611145949.2674086-7-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>