eth: bnxt: use the RSS context XArray instead of the local list

Core already maintains all RSS contexts in an XArray, no need
to keep a second list in the driver.

Remove bnxt_get_max_rss_ctx_ring() completely since core performs
the same check already.

Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Link: https://patch.msgid.link/20240711220713.283778-9-kuba@kernel.org


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