bnxt_en: enable interrupt sampling on 5750X for DIM

5750X (P5) chips handle receiving packets on the NQ rather than the main
completion queue so we need to get and set stats from the correct spots
for dynamic interrupt moderation.

Signed-off-by: Andy Gospodarek <gospo@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>