bnxt_en: Refactor RX VLAN acceleration logic.

Refactor the logic in the RX path that checks for the accelerated VLAN
tag by adding a new function.  This will make it easier to support
the new receive logic on P7 chips.

Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Link: https://lore.kernel.org/r/20231201223924.26955-9-michael.chan@broadcom.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>