eth: bnxt: move from .set_rxfh to .create_rxfh_context and friends

Use the new ethtool ops for RSS context management. The conversion
is pretty straightforward cut / paste of the right chunks of the
combined handler. Main change is that we let the core pick the IDs
(bitmap will be removed separately for ease of review), so we need
to tell the core when we lose a context.
Since the new API passes rxfh as const, change bnxt_modify_rss()
to also take const.

Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20240711220713.283778-5-kuba@kernel.org


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