bnx2x: Fix configuration of doorbell block

As part of VF RSS feature doorbell block was configured not to use dpm, but
a small part of configuration was left out, preventing the driver from sending
tx messages to the device. This patch adds the missing configuration.

Reported-by: Eric Dumazet <eric.dumazet@gmil.com>
Signed-off-by: Ariel Elior <ariele@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Tested-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>