bna: Add Callback to Fix RXQ Stop

Change details:
 - Add a callback in the BNA, which is called before sending FW command to stop
   RxQs. After this callback is called, driver should not post anymore Rx
   buffers to the RxQ. This addresses a small window where driver posts Rx
   buffers while FW is stopping/has stopped the RxQ.
 - Registering callback function, rx_stall_cbfn, during bna_rx_create.
   Invoking callback function, rx_stall_cbfn, before sending rx_cfg_clr
   command to FW
 - Bnad_cb_rx_stall implementation - set a flag in the Rxq to mark buffer
   posting disabled state. While posting buffers check for the above flag.

Signed-off-by: Gurunatha Karaje <gkaraje@brocade.com>
Signed-off-by: Rasesh Mody <rmody@brocade.com>
Signed-off-by: David S. Miller <davem@davemloft.net>