bnxt_en: Add bnxt_lookup_ntp_filter_from_idx() function

Add the helper function to look up the ntuple filter from the
hash index and use it in bnxt_rx_flow_steer().  The helper function
will also be used by user defined ntuple filters in the next
patches.

Reviewed-by: Andy Gospodarek <andrew.gospodarek@broadcom.com>
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>