bnxt_en: Refactor bnxt_set_rxfh()

Add a new bnxt_modify_rss() function to modify the RSS key and RSS
indirection table.  The new function can modify the parameters for
the default context or additional contexts.

Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20240325222902.220712-10-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>